The one where I re-invent something that's already patented.

For the last few weeks I've been working on a secret-squirrel 3-D printing project.  I thought I'd discovered an inexpensive way for folks to 3-D print metals at home.

It works.

It's cheap.

And today I discovered that someone else has already patented it.

I'm deflated.  Crushed.  Empty.