Very true. I was putting together a trainer kit a while ago and in the process, I failed to install a spar in one of the wings. Don't ask how I managed to do that, but I did. When I finished the wing, I noticed that I had one extra part.... the spar. Anyway, I couldn't do much about that, so I thought I'd buy a wing kit and just build another wing.

Well, the wing kit was about 20 dollars cheaper than the entire kit... so I bought another entire kit and finished the model with that. \

I had lots of spare balsa after that fiasco.

CGr.