Don't Punish Me if I Can't be Perfect

I got tired of people telling me, "You don't have to be perfect" and then punishing me when I'm not. It's not fair to be contradictory. Why tell someone that and then crack down harder on them when they mess up than on people who often mess up? I never understood that. It's like because I was pretty good, then when I made mistakes then I got slammed for it. But when my siblings who didn't care as much about right made mistakes, then it wasn't as big of a deal. (Obviously some times it was). But when discussing it, I learned that it seemed like a bigger deal when I did because I didn't do as much bad stuff. I don't know, maybe I'm off but it just seems that if you are going to expect things then you should expect them from all your children. If one disappoints you, it should be as big of a deal if the other does, not less. Why require more out of one?