mistakes in a metal shop are not "happy little accidents", but even so...

Sometimes you make some tool or widget and you have to leave in some small goof - a feature that is too wide or narrow, a small gouge or unintentional divot or hole that doesn't belong - because you've put loads of hours into the thing and fixing the goof would entail starting over.  So you leave it, but every time you see that goof mark, you wince a little bit inside, because your pride wanted it to be perfect.

Tom Lipton @ Ox Tools talked about this briefly in one of his recent Monday Night Meatloaf talks, and a reader in the comments left this gem of wisdom for us:

"A bozo mark is something I look at fondly in a tool I get / buy from somebody else. When we notice them, we get to feel a little of what the original maker must have felt. It is wordless communication between two people who may never have met, but are in the know." - Kenjiro5775