Or, when in doubt, cut it a little too long. You can always take more wood off. You can't put wood back on.
Redditor PangurBanHammer brings us this photo. Many commenters offer similar pieces of advice for different professions, as well as amusing ways to teach them. Babygrenade talks about the measure-twice rule in cooking:
My chef friend had a new line cook that overcooked a steak. He told him to stick in the freezer to uncook it a bit. The line cook actually did and then forgot about it, so my friend replaced it with a raw steak before telling him to check on it.