Question: what is the worst mistake you've ever made when engineering?

Nathan Quinlan answered on 8 Feb 2015:

I have broken expensive bits of equipment, lost weeks of work because I didn’t backup my computer, and sent important emails with stupid mistakes in them. My usual mistake nowadays is to try too pack too much work in a project. Mistakes are ok as long as you get them out of the way early before they do harm, and learn from them – and don’t repeat them!