i have learnt to not jam ya finger betwixt chain and big ring when fitting a new chain.....its pointless and very painful....also using ya head to slow the rate of descent when flying sans wings is also a dumbas thing to do.....
I've learned to put more planning into a build and buy parts that are co-ordinated instead of just buying the first parts that i find that will fit and do the job.
BITD the first frame i built up was a Zaskar LE (bought new), ended up with a load of cheap crap on it just to get it riding, also back then i didn't know there was a difference between gear and brake cable outers and ended up using one for the other, for a while i didn't know why the gears and brakes were so crap
What you think you are going to like does not always work out.
It is ok to change your mind.
You don't need a reason.
No one else has to understand or like it.