You're on vacation and you're reading Charles Dickens' "David Copperfield" and you're loving it. Every day is another chapter, another comic glimpse into the fates of David and Aunt Betsey and the Micawbers and Agnes Wickfield and even the nefarious Uriah Heep. It's a long novel - the Penguin edition runs 951 pages - and you're deep in the middle of it.

Now let's say you're napping on the beach, and when you wake up "David Copperfield" has been swept away by the tide. It's gone, you're in a foreign country and can't get a new copy, and you're stuck where you were: deep in the middle of it, without the satisfactions of plot resolution and emotional closure. It's unfair and you feel cheated, denied the deliberate finish that every good narrative provides, the denouement you need to "let go" of the old novel and begin a new one.Until the 1980s, when series TV finally discovered the artistic and commercial advantages of final episodes, that's where viewers often found themselves: deep in the middle of it. While it's unthinkable for a published novel or a movie to arrive unfinished, it was common for beloved TV series to simply disappear mid-story, their situations unresolved, the characters gone fishin' until they were lucky enough to return in syndication (or a ridiculous TV movie like "Rescue from Gilligan's Island"). Twenty years ago, "Seinfeld," which will reach its highly anticipated ending on May 14, would have merely evaporated. With the exception of the closing two-part installment of "The Fugitive" in 1967, which wrapped up four seasons of suspense about the murder of Dr. Richard Kimble's wife, TV consistently ignored or underplayed a basic rule of Western storytelling: The End. It wasn't until Mary Tyler Moore and her co-workers had their group hug in the WJM newsroom in 1977 that an age of well-thought-out series finales finally began, honoring and respecting the viewer's attachment to TV series and their characters.

Why did TV take so long to figure out that we like finales? Artistically, they are essential. The medium of TV has hugely powerful storytelling abilities, stringing narratives in real time across years. It's just sloppy to leave the strands loose, at a writing standard lower than that of other media. "Before final episodes, there was a sense that TV was never valuable enough to put the finishing touches on," says Syracuse professor Robert Thompson, head of the school's Center for the Study of Popular Television. "It was just this disposable drama we watch every week."

Emotionally, too, a lack of proper goodbyes on TV is sloppy, running counter to all our culture's enlightened prescriptions for healthy separation. The reality, good or bad, is that Americans are taking hours every week to bond with Ozzie and Harriet and Rickie and Lucy and Rob and Laura and Dharma and Greg. It's insufficient not to provide a chance to bid farewell to the characters they've visited loyally, laughed at, cried over and analyzed with friends for years. There are many heightened analogies - the death of a loved one without a funeral; leaving therapy without termination; abandonment by a spouse - and none is particularly positive.

Dr. Will Miller, an author and psychotherapist who serves as Nick at Nite's TV Therapist, says it may be a cliche but we shouldn't underestimate the emotional ties between viewers and their favorite TV characters. "So many millions of us have moved around and don't have extended family near us," he says. "So we feel much more interpersonal, psychological attachment to the people we've come to know on TV than in the past. . . .

"Consequently, when they go away, it's not just metaphor: People feel loss. They really do."

Finales also meet the emotional needs of the ensemble casts of the series themselves. Vince Waldron, author of "Classic Sitcoms," says TV stars like Jerry Seinfeld and Mary Tyler Moore are the executives making the choice to go out with a bang. "I don't think their primary goal in creating a final show is to serve the emotional needs of the audience. It's really for themselves. When you're working on a show five days a week for seven, eight, nine years, you're spending more time with the people on your cast than you are with your family."

Nowadays, final episodes have become objects of obsession and 1990s "event"-styled hype; they are media circuses of the sort that turned the night of May 20, 1993, into a distended goodbye to "Cheers," featuring a series retrospective, a two-hour episode and a soggy visit to "The Tonight Show" by some of the cast.

The night of May 14, 1998, may turn into an equally surreal event, as "Seinfeld" leaves the air after not only nine seasons but five months of intense anticipation. There will be a one-hour retrospective, a one-hour finale, and possibly a cast visit to "The Tonight Show," if NBC has its way. Even those who rarely watched the top-rated comedy will tune in, a fact that has helped the network justify a record-breaking $2 million for 30-second commercials during the finale hour. Obviously, the aesthetic motivations for closing episodes are matched by financial motivations.

The most successful endings offer a balance of sentimental catharsis, the tying up of plot ends and an absurdist flourish or a final, unforgettable image - all in keeping with the tone of the series. The last "Mary Tyler Moore" still stands as one of TV's model goodbyes. Sticking to the series's regular half-hour format, the episode was heartfelt but never gooey. As the characters bid one another farewell in a group hug, then left WJM, singing "It's a Long Way to Tipperary" with a stiff upper lip, viewers were able to do the same, vicariously. Mary took her final look at the newsroom where she'd made her surrogate family, then turned off the light, a quiet but memorable punctuation to one of TV's finest shows.

The last "M*A*S*H," on the other hand, was cloying and reckless as it drew 11 years of story to a close. Talk about the long goodbye. It was a half-hour show stretched far too thin over 2 1/2, attempting to be an intricately plotted movie instead of a direct and effective farewell. Fans gathered at "MASH" bashes on Feb. 28, 1983, for an ending, and instead they got a bundle of new developments, including Hawkeye's nervous break-down, Klinger's marriage, Charles's job search, the shelling of the 4077th, a group of Chinese musicians and more. Ultimately, the goodbyes were buried under all the goings-on, and they were weighted on the schmaltzy side.

The most talked-about endings have a clever twist, sometimes toying with the it-was-all-a-dream device that "Dallas" employed to explain away an entire season. "St. Elsewhere" ended in 1988 after six seasons with a jarring zinger, as the whole show was revealed to have taken place in the imagination of Dr. Westphall's autistic son. While some viewers were mystified, and others felt it negated the life of the show, the twist stimulated thoughts about fiction, reality and the television medium.

The most uproarious and surprising finish was for "Newhart," in 1990. After a few bizarre plot developments - the town was remade into a golf resort by Japanese developers - Bob got knocked out by a golf ball, and woke up in bed next to Suzanne Pleshette, his wife from his previous series, "The Bob Newhart Show." All of "Newhart," which lasted for eight seasons, had been the dream of a character from another sitcom.

Last year, "Roseanne" ended its nine-year run with a scandalously rickety version of it-was-all-a-dream - an approach that will forever be difficult to use after "Dallas" and "Newhart." The idea was that the final season, in which the blue-collar Conners won the lottery, was all fiction written as therapy by Roseanne after her husband, Dan, died of a heart attack. But, confusingly, some of the last season was real, like Darlene's baby. As one fan nicely articulated it on a "Roseanne" Web site the morning after, "It is like watching friends move away, and then finding out that they lied to you and you never really knew them."

A poor ending like the "Roseanne" finale doesn't help a show's popularity in syndication, says Dr. Miller. "When you create a warm ending, you keep the characters alive for people, and I suspect that affects people's loyalty over the years. . . . Say you have a beloved uncle and you didn't know all the details of his life. You just knew that to you he was kind and warm. And then you go to the funeral, and the eulogy exposes all this horrible stuff. What you want is to go to the funeral and have others give voice to the same feelings you have. That's his final episode. It brings closure."

And when it's all said and done, "final episodes" are actually provisional, goodbye-for-now episodes, since most long-running series take on second and third and fourth lives in syndication. When "Mary Tyler Moore" ended, Esquire asked former series regular Cloris Leachman about the meaning of the event. "It's not as though we're saying goodbye to Mary Tyler Moore forever!" she responded. "After all, the show will go on into syndication forever."

Leachman was more right than she knew in 1977. Not only do classic TV shows rerun endlessly now, but they become institutions on TV-museum channels like Nick at Nite and TV Land; they become the objects of fetishists at Internet Web sites; they become theatrical and made-for-TV movies.

It's this growing industry around classic TV that makes final episodes more possible, says Thompson. "Just as a belief in a religious afterlife allows you to say goodbye at a funeral and know you will be rejoined with this person again, Nick at Nite and TV Land and syndication have allowed us the catharsis of a good cry at the sappier endings or a good laugh at the funny goodbyes, knowing that the next day we're going to be able to rejoin these people again, if in a slightly stale fashion.

"If there were no syndication and we were leaving these characters forever, final episodes might be a little hard to take."