Rule of thumb

A rule of thumb is something specific to a particular activity. It teaches something and makes it easier to remember at the same time.

As a woodworker, the first thing one is to learn is "Measure twice - Cut once". Because you can always cut more off. But you can't put it back if you cut too much.

What is a Rule of Thumb in your area of occupation or interest? The readers of this blog are interested.

Let your knowledge be known. Post your Rules of Thumb in the comments here. Even if it's just a link. We want to know. All topics are worthy. Go ahead and post it.