For me, i feel it's the opposite (not only for jams, but from everything, really): I tend to do great the first time i'll do it, and then i'll just do worst and worst, get really sad about it, and then... quit
This is the first time that i openly talk about it, since i really like making games (it's a thing that i always wanted to do, and one that i want to transform into a job, if i can manage to do it) and i'd really like to not end up like everything else end up so far...
As for the the "concept part", the answer is pretty much what i've already said to menicafolden: that's exactly one of my struggles. I've kinda liked the last part of your answer tho. :3
Thank you, i hope good luck to you too, and thanks for the kind words!!!