Only lend a friend what you could lose without losing them too.

Money between friends works until it does not, and when it does not, the friendship pays. The amount matters less than what happens inside you while it is unpaid: a small ledger starts running, every purchase of theirs gets noticed, and the thing quietly becomes about something other than the money. Few friendships carry a long resentment well.

Set your own ceiling before you are asked, at a number you could write off without a flicker. Give rather than lend where you can. If the amount is above the ceiling, you can decline the loan and still help in some other way.