What's the costliest mistake you have made? What was the aftermath?

My boss bought a 100 kw generator to install in place of a 45 kw unit. I protested and explained that despite the base load not changing the average heat rate from the aftercooler would increase the cooling requirements above capabilities. It was close to $12,000 for me to install a pump, temperature controller, heat exchanger, and piping to rob cooling water from the main engines if the generator overheated. The generator set was only $30k. I made them buy a $5500 Viega Megapress system to install the piping because I'm not a welder. This was cheap considering I had to come up with the plan, spec the heat exchanger and pump, spec the piping, build the temperature controller and install everything all without downtime.

/r/AskEngineers Thread