I can only share my experience and flawed calculations in hopes to save others the same.
I too have cut down many widow makers. The more I tend to cut down safely, the more I found myself reasoning that I got the math formula down and safety strategies in place, until that ONE day......
I woke up after being knocked unconscious. I never had a warning or saw it coming. The only way I knew I got knocked unconscious was finding myself flat on my back, safety helmet and face shield laying 25' to the left of me, chainsaw still running 50' behind me, and myself now 10-15' away from where I was last standing cutting the tree......and the fallen tree Fortunately 180 degrees in the opposite direction of me.
When I inspected the tree, I noticed the heavy leaning over into one direction, and marked where it "should fall", given gravity, it's 20+ degree lean, the heavy tree limbs, etc. I clear cut two safety paths away, and pre-planned where to drop the chainsaw for protection and in which direction I would run, it was a 140' plus tree, so I was planning on getting a good safe distance away from it at the slightest movement it would show, lots of surrounding trees of different heights.
The tree was leaning against another tree, and when I cut it, I mis-judged/calculated the shear spring tension stored in it and the direction it would release. Not only was there tremendous spring tension in it, but it had a twist in the tree. Instead of the entire tree untwisting itself, only the bottom part did so when I cut it, since the tree branches were caught between the other trees. Before the tree showed any signs of starting to lean over more, it just sheared/tore the remaining of the tree trunk and hit the chainsaw out of my hands, and scraping 1-2 layers of skin off my forehead and knocking me out in the process. I only was able to piece this detective puzzle out after getting back onto my feet. Needless to say, I called it a day after that close call! The chainsaw still running in the back was the scariest after thought. No nightmares as of yet ;-)