Here's one for every formwork and framing site.

Level accuracy is critical when a project is in it's infancy stages because it can cause so many problems later if the bones aren't accurate.

Can't tell you how many times I've seen guys step on, drop, kick or trip over a level. That level may get put aside for the rest of the day but if it gets picked up the next morning and isn't checked, frustration is on it's way.