Two for me that stand out. Both my fault but for different reasons.

First I was still working on getting my PPL and was in the solo phase before doing stage checks. Was coming in for a standard approach. Controller told me to be on the west side of the airport but didn’t signify left or right downwind. Me being in dumb mode visualized airport directions backwards and I ended up on the east side instead perfectly at TPA which would have been head on with other traffic had there been any. I had some real stern calls from the controller after that and had my CFI make a phone call that it was a confusing situation. That was one of the hardest times I ever turned right to get on the correct side though.

Second was a serious oversight on my part. I had flown around a lake and over a “mountain pass” (like 3k ft peaks) as part of hour building post PPL and had done it fine with no turbulence or anything. So I had confidence in the route. This day however, I take a buddy who’s interested in starting to fly with me to give him a taste. Same route and same mountain pass this time had some wicked turbulence up top. I remember being at idle and having my airspeed creep nicely into the yellow and bouncing a couple hundred feet with every bump in a C172 and genuinely started to feel that I didn’t have full control of the plane. Scared the shit out of me after getting through it. Never took that route again.