I would guess the tricky thing with bikes are all the similar looking metal bars at different angles. It’s hard to perceive the overall shape of the bike and re

I would guess the tricky thing with bikes are all the similar looking metal bars at different angles. It’s hard to perceive the overall shape of the bike and remember how the pieces are connected. So maybe other similar things that are assembled from several parts would be hard: a folding chair, a pair of scissors, a suspension bridge, the Eiffel Tower, a catapult, etc.