And if you can't do 40, do five. And if you can't do straight pushups, do knee pushups. And if you can't do five, do one. Then two. Then five. Then 40. But don't rush it, just do what you can and then a little more.
Seconded. People often get overwhelmed at the scope of "become more fit" once they've finished a workout or two. Doing it one small accomplishable bit at a time is a totally valid way of building a fitness habit, and is NOT something to be ashamed of. And for the RPG nerds here this is exactly how you level-up IRL.
Oh, man. How long I gotta spend level-grinding at the gym? (whah! :-))