Stumbling is OK, people do that too occasionally, but not being able to get back up on his own is a far larger problem with Asimo IMO.
(Ohh, and the fact that it walks like a semi-drunk person who soiled his pants).
Errors are excuseable (and unavoidable), not having a recovery strategy in such a million dollar project is not!
Even my 16 months old grandson can do better in that department (not walking stairs, but getting up whenever he tilts over).
Start off with a stationary body, moving a single arm or turning the head a little can make a powerfull impression when onlookers think they're looking at an inanimate object.
Then improve a little bit at a time gaining experience and soon you'll be the talk of the town, but making a fully fledged and convincing android is likely not gonna happen on a hobby budget or by a single persons work.