Back in '09 I thought a propane forge was just a cheap shortcut for hobbyists.
After borrowing my friend's Johnson gas forge for a month in my Portland garage, I was shocked by how clean and even the heat was for most of my general forging work, so what's one tool you were totally wrong about at first?
My old boss at the machine shop swore by files for finishing. I thought they were slow and outdated compared to a belt grinder. Then I had to fit a custom bronze bushing by hand. A few minutes with a smooth mill file gave me a perfect press fit that power tools would have ruined. I keep a full set in my box now.