I was wondering how come..?

famous musicians never mess up? i mean i know they practice lots and lots but still, how can you not mess up every once in a while? expecially if your new at being famous? sorry its worded weird. and i mean with singing and playing an instrument.

professional do mess up. Lots! But we in the public are so jazzed by what they are doing that we don't notice it much. Only another professional might, and that out of experience.
We are really spoiled in this day and age: we have captured so many performances on tape,CD, computer, and they are usually so well recorded,mixed, and spliced, that we get nothing but a perfect performance every time.
Live isn't like that at all. Live means dealing with a cold, an acoustically bad venue, co-workers in a bad mood, music that you don't necessarily like ( in the classical world, we don't often get to choose, we are told what to perform), and a whole bunch of other factors. Obviously, a well-trained and disciplined performer willl get past most of that, but it's that edge of "you never know" that allows mistakes to creep in, just where you don't expect/want them to happen.
We do get over mistakes ( you have to to keep the music going) but you never run out of things to learn!

I don't know, that's a great question. A lot of famous singers lip sing during concerts *cough*brittany spears*cough*

I dunno, it's weird
I tried to sing and play my piano at the same time but it's very hard to me

I'm sure they mess up at times, but fans don't really notice. They might even stumble onto something that sounds better to them.

Oh, Elizabeth...It would be very cool to never make a mistake or goof up once in a while. Especially after the practice most artists put into their work...but please trust me, it's not that they don't mess up. They do. & many times. It's just most of the times they can cover it up so well (back up singers, dancers, play-back, no video cameras in concerts, etc...), no one really cares. Now, I'm not saying that no one notices. I myself have noticed. But most of the times they do such a good job that a mistake here and there doesn't matter!! I hope you understand! & that you relate to my answer!

They rock (pun not intended) and they know what they're doing (including how to fix a mistake).

[They also have agents and managers who can DO THINGS ;)