the rix mix

One of the reasons late-night shows go so horribly wrong so often is that the physical toll of the job is different from other gigs. It requires stamina, psychic isolation and an inability to get bored.
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Jay and Conan both have this stamina, and it's extraordinarily rare. There are only a few guys alive who have the freakazoid DNA to do the job.

Rob Sheffield, "Late-Night Bloodbath," Rolling Stone

Overlooking daytime hosts, who may have a worse grind. Not only the family dysfunction show hosts. It's probably a psychological stretch for Ellen DeGeneres to be up up up every day, if her stand-up was halfway honest. She seems like a person who has good days & bad days. Her comedy was always a bit down, depression shadowing it, her delivery largely deadpan. Unlike Rosie O'Donnell, Ellen's show isn't designed to permit bad days, lousy moods., & open aggression. Maybe it's why Ellen has a dance-your-blues-away ritual. On one of her rare promotional appearances as a guest with Letterman, she talked about needing to get used to feigning interest in boring actors shilling bad movies, & tolerating celebrities who are clearly unintelligent. She hadn't fully comprehended how difficult it would be. As an experienced stand-up comic, Ellen - like Leno - is a tough cookie. Daytime talk is littered with more notable failures than late night, but the shows were canceled faster & failed more quietly. Some just faded away. Daytime success is an achievement.

Doing 3 or 4 mostly talk hours on radio five days or nights a week is a grind. You have to love radio to do it. Only a relative handful of radio hosts are paid big time money, management is bottom line ruthless - they make NBC execs look like class acts.