In my early 20's I lent money to a close friend; approx $500. She stated she'd pay me on a specific date. That day came and went. Almost a year later I was repaid. It certainly fractured our friendship. Not b/c of the money, it was the... I promise I'll pay you on this date, then nothing.
This was the only time I lent someone money. Made it easier to say no. Years later she asked to borrow money. I replied, I learned long ago not to lend money....