Do you watch 'Louie'? It's an often very offbeat, dark comedy about a divorced stand-up comedian who lives in NYC, and it's written, directed by and stars Louie C.K.
Joan Rivers is in a recent episode, and is just amazing! She's got a great scene where she and Louie talk shop that is candid and blunt about a comic's career path (and could be applied to an actor's).
I can't find a link to the excerpt, but the 20 minute episode is really worth watching. It's on Hulu for probably the next two weeks or so. Probably available longer if you've got Hulu+
Note that Louie is TV-MA - language in this episode is definitely NSFW.
If you don't have time to watch the episode (or are reading this post after the episode link expires), here were my takeaways from Joan and Louie's conversation.
1) this business sucks - you go up quickly but back down just as quickly. And just when you think you've got it all figured out, some kind of game changer happens (like Betty White!).
2) But if you love it, you love it and you're called to do it, so you do it anyway.
3) Probably the best bit - learn people's names while you're on your way up - you'll need those people in your corner when you're on your way down.