There is a saying in the studios... "Make Loud Mistakes."
When you are recording, whether for a CD or TV/film, time is money. (Another saying.) Often when a musician is playing an unsure section of a chart or song he plays softer. It's completely natural to be timid when one is laking in confidence. This is a problem on two fronts.
First if you make a mistake at this lower, shyer volume, it's very likely to go undetected, even by you. That is until you've packed everything up and they are mixing either later in the day or weeks later. A conversation usually follows. Something like this...
"Did you hear that?"
"Yeah, who was that?"
"I don't know. Solo the keys."
"Nope, not him."
"Yep, there it is. He's a half step off in that bar isn't he?"
"Can you just mute that bar?"
"Let's see. No, now the guitar just drops out for a bar that doesn't sound right."
"We're going to have to replace the track."
"This needs to be done today."
"I'll make some calls, it's going to cost us to get someone in here today. I won't call that guy again."
Had the guitarist in this scenario made a loud mistake it would've been fixed then and there. All would've been forgiven. It is my hope that I have not caused this problem. I learned early to make loud mistakes.
Secondly, it's a problem because when a player is afraid to make a mistake he plays timid not with confidence. This does not make for a compelling guitar track. The best session players are all in when they are tracking. If you are OK with the occasional loud mistake you'll be more likely to create a part that worthy of burning onto a disc or airing on TV.
So when you are laying down guitars on you next session make loud mistakes. Chances are you won't make any mistakes and your tracks will sound much better and much more confident.