Prodest Amor et Obest
Est uni iucundus amor, nocet alteri amasse;
Quodque uni prodest, alteri obesse potest.

The vocabulary is keyed to the DCC Latin Vocabulary list. There are only two words in this poem that are not on the DCC list:
iūcundus, -a, -um: pleasant agreeable
obsum, obesse: be an obstacle, hinder, hurt
alter altera alterum: other of two
amō -āre: to love; amans -ntis m./f.: lover
amor -ōris m.: love
noceō nocēre nocuī: harm
possum posse potuī: be able
prōsum -desse -fuī: be of use, do good, help (+ dat.)
qui quae quod: who, which, what / quis quid: who? what? which?
sum, esse, fuī: be, exist
ūnus -a -um: one