A tale,
Many moons ago when I was a young and inexperienced gliding instructor one of the less self confident pupils came to me and told me about the difficulty they had experienced in trimming the glider they had been flying that morning. The person was very light and the thermals that day were quite powerful.
So the gathered masses had a long discussion about weights, trimming and a load of other possible explanations why this glider (a K23) would have been difficult to trim.
A very old and wise mechanic walked off with some tools to the cockpit removed the seat pan and found..........a screwdriver!
This was lodged in the the trim mechanism.
We did a quick testflight to confirm all was well and subsequently the student flew the machine as well again confirming that there were no problems anymore.
I learned about flying from that.
FD