I was making a new sled for the table saw that addressed some
deficiencies I'd found in the old one. One thing I wanted to to was
make it longer front to back so I could put the fence in from the part
that I pushed with that I wouldn't be leaning over the saw at the end of
the cut, and to help keep my hands away from the blade.

So I carefully measured and cut a piece of Baltic Birch for the base,
marked it up, and was all set to start drilling and routing various
slots and holes when the awful realization dawned on me--while I had
precisely measure it, I had precisely measured it THE SAME SIZE as the
one I was replacing.

Lesson learned: Think first, before you measure.

Didn't cost me anything but a little bit of plywood that I'm sure I'll
find a use for eventually, so it's a cheap lesson, but I figured it was
worth sharing.