I've got two bone head lessons learn to share...
1. When I first started into making knives, I had no idea about heat treat aside from getting it red hot and quenching. So I bought a bar of O1 (because I heard it was really easy to work with) and ground my knife almost to complete finish.... sharp edge and all. Then I thought, "I want this to be the best knife in the world." So I clay coated the spine, heated it up as hot as I could (yellow) and quenched it as fast as I could (in a bucket of iced water). The sound that came from that quench was like nothing I've ever heard..... I truly made myself a worldclass knife that day.
2. My wife is a graphic designer for Parks Canada and was working on a sign that was mounted on an aluminum plaque. I refaced it for her on my grinder, then went about my business as a knifemaker. I discovered the recipe for thermite that day, along with how to ignite it.
Rick