On the family side, a lesson I learned long ago is to never loan money to a friend or family member more than you are okay with losing.
If I lend money to family or friend, in my mind I assume I will never be repaid. It makes my life much better.
Actually, I will tell them: "I am giving you this money".
The only time I said it was a loan was when my ex-wife asked me to "lend" her some money, which I did, telling her I hoped she'd pay it back as soon as possible
(I knew she never would.)
Since then, she takes pains to avoid me.