Ná cuindig do chís ...

Ná cuindig do chís
for duine nad·fóel
is ferr úad a lleth
andá a meth mar óen.

(not * seek * your * rent
on * person * that will not bear
is * better * from him * the * half
than * their * failure * as * one)

Seek not to collect tribute
from one who cannot pay;
better to accept half from him
than to lose both man and money.

The word "cís" can mean "tribute, tax, rent" in Early Irish. This bit of advice to a prince, stanza 13 of "Cert cech ríg co réil", seems to fall somewhere between "you can't squeeze blood from a turnip" and "don't kill the goose that lays the golden eggs".