Which profession has absolutely no room for ANY **** ups?

Source.

@Sparky: Pilot and a Surgeon

Lion tamer
Air traffic controller
Cell tower installer

My job lol trimming trees around 345 thousand volt power lines

Lol.... Yes.... Also probably working on bridges and that line of construction work, paramedics, semi truck driving, those who make their living swallowing swords, eating nails and fire, exploring wild animals, and bungee jumping/parachuting. Car racing seems to also be one I wouldn't want to screw up with either.

Building a foundation can not have any mess ups either if any thing goes wrong the entire house can collapse

NASCAR racing. I used to be into it till my driver retired and I know what some are thinking, "they just driving in circles, oh yep another left turn". It takes a lot of skill and balls to go 190+ Mph inches away from 41 other drivers AND still hold you're line and not wreck the entire field

Rocket scientists

@XsanteeSouthernManX:
Thats a good answer because if the foundation is screwed up and not done right it throws the whole construction of the house or building off