Dev lesson learned the hard way. Never rm -rf with wildcard arguments... If you think you're being clever it probably means you're about to mess up some shit.

Fear holds you back...

Same for poorly designed databases with delete and drop table. A good habit is to always always double check before you execute. Fortunately I have never made such a mistake but I have seen others do it. Then I realised I didn't want that to happen to me so since then I always double check and that works quite well.

People ask me how i became a programmer?
I executed rm -f *.*
Easy