If you're not stubborn, you'll give up on experiments too soon. And if you're not flexible, you'll pound your head against the wall and you won't see a different solution to a problem you're trying to solve.
When making something, always get a few extras — extra material, extra parts, extra space, extra finishes. The extras serve as backups for mistakes, reduce stress, and fill your inventory for the future. They are the cheapest insurance.
The harder the battle, the sweeter the victory.