When do you know if you're truly ready for a baby?

I know a lot of people will say, 'If you have to ask that, you're not ready.' But I don't know if I necessarily believe that. Plenty of people TTC and then say they don't know if they're ready to be parents. I don't know of they should be doing that, but.. 

I know most people freak out about being good parents. But that's a good sign, right? They're worried about being the best parent they can be for the child's sake? 

My husband wants to begin TTC, but i'm just worried I can't be selfless enough. 

Advice? Past experience?