Why can't i go a session without making a mistake?

[Alex424]

I play a decent standard of poker, and i'm sure i am a winning player and my stats and results read good.

BUT, why do i keep making 1 or 2 mistakes in say a 2 hour session. I'm not saying i don't make other mistakes as i'm not Phil Ivey. What i'm talking about are mistakes where i know what to do but for some reason i make a different play and realise its the wrong play as soon as ive made it.

SOOO frustrating as i know its eating away slowly at my win rate.

Is this common? Is it rare to go a session without making what should be easily avoidable mistakes.