Minor things I've had, Gear not coming down, electrical failure (VFR), fire in the nose cone of the Seneca (lead wire to the battery terminal shorted out causing the insulation around it to catch on fire) Didn't know about until MX took it apart and looked inside. Other things, icing, getting too close to T-storms, very strong mountain waves that made the stall horn off. That was trying to go to BTV. I will not fly over the mountains in anything less than a cherokee 6 and no lower than 8,000. Fortunately most of the "stupid" things I did to get myself in those WX situations I did in my first 500hrs of flying. I learned a lot back then. Then I became a CFI and learned whole lot more but I have say I am glad made all those mistakes on my own not trying to teach someone else.