Or they can be quite vexing, especially if the "puzzle" in question is a Marlin Model 1894 lever-action carbine like the one that I took apart to replace a bad carrier due to a Marlin design flaw. It's even more fun when you reassemble it and find a part on your workbench that you absolutely don't recognize as ever having come out of that rifle.
Whoops. Cue the clown music. Now take it back apart and figure out where that mystery part* goes.
I did finally get it back together after about twenty minutes of fumbling, though, and bonus points: it functions! Now I'll just have to wait for the next range day to test it out.
Once again: Thanks for nothing, Marlin.
* said part was subsequently identified as a "locking bolt", and like the carrier I was replacing, it's another one of those "restricted" parts that Marlin would have refused to sell me had I lost this one and needed to order a new one. That's the main reason that you should buy Henry or Winchester rifles when you're in the market for a lever gun.