Why am i so athletically inconsistent?

I love sports. You name it I will play it. I am by far not the best though. I am really kind of mediocre, now I don't let that stop me! Just like everyone I have my good and my bad days. But it appears to me I have more like good and bad minutes. every coach i have ever had has said my problem is my inconsistency, i can almost never do the same thing twice. I have tried and tried and tried and guess what? tried again! all to never get it right but maybe one time out of ten. and i cant replicate that one time! i partly think it is mental but partly think it is just my muscle memory is out of wack or something! i really don't know! Please give me some advise! id appreciate it very much!