I once built a data import tool using F# (It was a .net shop). I left for another position and my intention was to help them with consulting-style work, but my

I once built a data import tool using F# (It was a .net shop). I left for another position and my intention was to help them with consulting-style work, but my next position was more demanding than I anticipated and my former company was forced to deal with it. I consider it one of my larger mistakes. In hindsight the real problem was building the thing in isolation and then dumping it on someone else with minimal training time. I think different tools and languages are fine, but they need a bus factor of 2-3 to prevent this kind of stuff.