As a 30-something hour PPL student, 'confession of mistakes' is the only area where I can safely contribute :-)
On one early solo I took off in a PA-28 without switching on the boost pump. Of course the mechanical pump kept going just fine, but it make me think when I switched it off at the top of the climb and found it was off already. Subsequently I built up a bit of drama-free solo time - and then a few weeks ago I had my first dual trip for a while and made a total dog's ***** of the checks (forgot to check the boost pump before engine start, forgot to change tanks before run-up etc.) My instructor let me get it wrong until just before we moved onto the runway, letting me see if I would pick it up - which I did, but only just in time.
It was one of those occasions where the whole school was running slightly late and I felt under self-imposed pressure to get moving quickly. Now, whenever I feel that same pressure, I try to actually slow down a bit, and do things properly first time rather than badly twice.