What was your silliest mistake made in business?
I didn't pay my domain name renewals in time? Everything is down at the moment. I feel soooo silly for not doing something so simple on time and as a result I have to deal with all the consequences.
Mine would probably not remembering when tools and software transition from the discounted promotional or trial rate to the full price. I'm constantly shocked at bills going up, but it is just because I don't keep good track of when those billing cycles and rates change. I'm working on improving this by keeping a spreadsheet.