Conan O’Brien made a triumphant exit from NBC Friday night, accompanied by one of the most impressive outpourings of support by younger viewers that any late-night host had ever seen  and Mr. O’Brien was effusive in his thanks for their backing. 
 
 But he might have said: Where were you when I needed you? 
 
 In the tumult that surrounded NBC’s late-night shake-up last week, one thing was certain: If even a small fraction of the additional younger viewers who flocked to Mr. O’Brien’s show last week had turned up regularly in his earlier ratings results, he would almost surely still be hosting “The Tonight Show.” 
 
 Instead, for most of this past fall, Mr. O’Brien struggled to command the young viewers he needed to counter a falloff in overall audience numbers. 
 
 While he began to drop behind his chief late-night competitor, David Letterman on CBS, among total viewers, it was more alarming to NBC that Mr. O’Brien was not consistently beating Mr. Letterman in several important advertising-sales demographic groups  viewers 18 to 49 and 25 to 54. (He did beat Mr. Letterman virtually all the time in the 18-to-34 group.) 
 
 But to NBC’s surprise and disappointment, Mr. O’Brien fell behind his predecessor, Jay Leno, even among those 18-to-34 viewers, the group expected to be his core constituency. (From his start in June through the end of 2009, Mr. O’Brien averaged 716,000 viewers in that age group, down from the 759,000 Mr. Leno averaged the previous six months.) 
 
 Several television researchers said in interviews that this outcome might have been easily predicted, not because Mr. O’Brien does not appeal to younger viewers  he clearly does, as evidenced by the large numbers he attracted for his closing shows  but because regularly assembling those young adult viewers in significant numbers in the late-night hours has become a daunting, if not impossible, task. 
 
 “The 18-to-34 group is so difficult to attract and the lower half, 18 to 25, is the hardest of all,” said Jack MacKenzie, the president of the millennial strategy program for the research firm Frank N. Magid Associates. 
 
 Compounding the problem, said a senior research executive for another company, was the fact that Mr. O’Brien was especially appealing to young men. “And that group doesn’t watch television very regularly,” said the executive, who asked not to be named because his business competes with NBC. 
 
 Instead of watching Mr. O’Brien most nights, Mr. MacKenzie said, those young viewers have been watching everything from similar shows like “The Colbert Report” on Comedy Central, to cartoons on the “Adult Swim” franchise on the Cartoon Network, and the ever-present array of sports and sports news on ESPN and its sister channels. 
 
 In comparison with the 719,000 viewers in the 18-to-34 group that Mr. O’Brien had been averaging, Stephen Colbert on his “Colbert Report,” in the same six- month period in 2009, averaged 746,000 viewers ages 18 to 34. The cartoons on “Adult Swim”  mostly “Family Guy” and “Robot Chicken”  averaged 619,000 of those viewers. ESPN from 11 p.m. to 1 a.m., with varied programs that included both live sports events and editions of the highlights show “Sports Center,” averaged 614,000 viewers in that group. 
 
 And dozens of other cable channels took other slices of the under 35 viewers. 
 
 “What you’ve seen in recent years is increased spending by all these cable channels for original programming,” Mr. MacKenzie said. “And besides having a double revenue stream of subscription fees and advertising, the cable channels have the luxury of targeting specific audiences. Broadcasters don’t.” 
 
 Fans of sports, for example, were watching ESPN many nights instead of Mr. O’Brien; and cartoon lovers were hooked on “Adult Swim.” 
 
 But even all the competition on cable did not represent the total distraction for young viewers that Mr. O’Brien had to contend with. The senior research executive pointed to outside attractions like video games that vie for the attention of young, especially male, viewers. And CBS executives have in the past identified the growing tendency of owners of digital video recorders to use the time after late local newscasts to play back programs recorded earlier that night or on previous nights. 
 
 A spokeswoman for Nielsen Media Research pointed to a study the company released last year that cited the peak hours for DVR playback. The late-night hours showed the highest percentage of playback outside the prime-time hours, with about 7.6 percent of playback taking place from 11 p.m. to 12 a.m. 
 
 As an executive from one of NBC’s rival networks put it: “Conan didn’t just have to worry about Letterman; he had to worry about ‘House.’ People are playing back episodes of shows like ‘House’ in late night.” 
 
 Add to all the other issues the fact that Mr. O’Brien’s young fans did not really have to watch television to see him. His shows were made available later on Web sites like Hulu. And his best comedy bits would frequently be posted on other sites  and passed around by fans  shortly after they appeared. 
 
 Mr. MacKenzie added that NBC did Mr. O’Brien no favor by moving Mr. Leno to the 10 p.m. hour this fall. “That meant there was a show very similar in style to his on the air before him,” he said. 
 
 In his run on “The Tonight Show,” Mr. Leno managed to attract the largest audiences in virtually every age group, though his ratings too showed signs of falling off in his later years on the show. But his was always the first show of the late-night talk variety on NBC each night, Mr. MacKenzie. 
 
 That will happen again when Mr. Leno returns to “The Tonight Show” on March 1. But Mr. MacKenzie had some words of caution for NBC. 
 
 “A generational switch is coming,” he said. “The baby boomer audience that has mostly been the Leno audience is going out. The Conan audience is becoming more influential  even if they aren’t watching television the same way the previous generation did.” ||||| Conan O'Brien is wishing he had been nicer to Ryan Seacrest. 
 
 "I thought about something today," he said Thursday during his penultimate monologue as host of The Tonight Show. 
 
 "Over the years I've made a lot of fun of Ryan Seacrest, Larry King, Spencer Pratt, Geraldo, David Hasselhoff, Kirstie Alley and Donald Trump. And here's the messed up thing—they all still have shows." 
 
 "As you all know by now, tomorrow is our last show here," he said. "I'd like to apologize to the guests that were scheduled for next week: President Barack Obama, the pope, the queen of England and our good friend, Elvis Presley." 
 
 While it's common knowledge that O'Brien signed a $33 million deal (plus $12 mil for his staff) that prevents him from suing NBC for breach of contract and requires that he not assume late-night hosting duties for another network until Sept. 1, the deposed funnyman let slip a few other stipulations in the agreement he inked today: 
 
 • "I am prohibited from coming within 500 yards of 11:30." 
 
 • "I must return the Etch-A-Sketch my contract was written on." 
 
 • "I'm not allowed to make fun of NBC programming. I have to let the programming speak for itself." 
 
 • "The cop who escorts me off the lot after my last show must have the rank of lieutenant or higher." 
 
 • "Max Weinberg must surrender his key to the women's locker room at the NBC gym." 
 
 • "Have to watch at least one NBC show every weeknight in order to double ratings." 
 
 • "Effective today, NBC will stop paying for Andy Richter's medical marijuana, and medical Jack Daniels." 
 
 • "Must stop production on my documentary expose of NBC: Inside the 'Cock." 
 
 So long as his freedom isn't hindered any further than that, O'Brien should be happy at Fox whichever network he ends up. 
 
 "Obviously this was not our first choice—it wasn't our eighth choice—but I'm determined to make the best of this situation," he said. "So, ladies and gentleman, and people watching, here is the plan. Tonight and tomorrow night, we are going to have a lot of fun on television, that's what we're going to do." 
 
 Before scheduled whirling dervish Robin Williams appeared, Pee-wee Herman showed up to act out the NBC-Conan feud with a stuffed peacock and a giraffe with a mop of red hair attached to its head, and Ben Stiller presented his own highlight reel of the Tonight Show With Conan O'Brien's best moments. 
 
 Of course, it only consisted of a montage of Stiller's appearances, but still. It's the thought that counts. 
 
 Adding to the elegiac tone of the evening was Jimmy Fallon, who had nothing but great things to say about Conan. 
 
 "If there's one thing I've learned from David Letterman and Conan," he said of his Late Night predecessors, "it's that hosting this show is a one-way ticket to not hosting the Tonight Show." 
 
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– Conan O’Brien joins the ranks of the unemployed today, so the ousted Tonight Show host now has plenty of time to track the backlash and second-guessing about the TV shell game. Jay Leno remains the villain of the piece, but the hard truth is that O’Brien never drew the numbers of young viewers to his time slot that NBC had hoped for. “The 18-to-34 group is so difficult to attract and the lower half, 18 to 25, is the hardest of all,” a strategist told the New York Times. The increasingly fractured TV landscape didn’t help. Competition is now fierce for the audience Tonight Show producers once took for granted. O'Brien has been buffetted by the same economic realities most American are grappling with, making him a "Harvard-educated, multi-millionaire late night talk show host" who was "magically transmogrified into a guy who got laid off at the local car plant," blogs Michael Ian Black.