You get to that point, with the thing hung on the lamp limiter, the startup kicks it over a few cycles and the lamp flickers. You think, maybe I should take that out of circuit now as it's obviously being throttled too much, so you put hard mains on it and PHUT. Then you think, why the fork would I take it off the limiter when it so obviously isn't working yet.
My worst disaster was actually not my fault but it felt like it. I had just overhauled a dead channel in a big vintage Pioneer receiver that uses unobtainable vintage ring-emitter transistors. It was all good, I set up the bias, took it off the limiter, moved it across the room and plugged it into full mains. In the process, the bias string had gone O/C at a lifted track on the board and it immediately ate all six output devices worth £50-75 each. Problem was, I had just bought a set of six to repair a channel in someone else's unit, and couldn't get any more as sources are few and far between. I had to settle for the older spec device with lower Vceo that was used in early production.