The Modern Translation
Polonius is a bit of a windbag, but on this point he is right. Notice what he says: a loan loses both itself and the friend. The $300 is the smaller casualty. Once Dana owes you, every future brunch carries a quiet ledger. You notice when she orders the second mimosa. She notices you noticing. The 15th arrives, then passes, and now neither of you mentions it while splitting an appetizer. So the useful move is to decide in the parking lot, before the keys leave your hand, what this actually is. If you can part with $50 and never think of it again, give it as a gift and say so plainly. If you can't, say no kindly, and say it fast, because a long pause reads as a maybe. Either answer protects the friendship. The only bad answer is the loan you resent, the one that turns a person you like into an unpaid invoice.
The Text-Message Version
Try It Today
Before anyone asks, pick your number today: the most you could hand a close friend and truly never expect back. Write it in your phone's notes. The next time someone asks for money, offer that amount as a gift or politely decline. Afterward, notice how your shoulders feel at the next dinner together. Without a ledger running, you should feel noticeably lighter.