A pearl of wisdom
Definition 1 of 1
Pro Tip 1/3Figurative Treasure
Understand it's a metaphorical treasure (like a real pearl) used to signify valuable advice. 
Every time we meet, he finds a way to give a pearl of wisdom.
Pro Tip 2/3Singular Use
Used singly, highlighting one important piece of advice, rather than a collection. 
In our talk, his pearl of wisdom about time management stuck with me.
Pro Tip 3/3Positive Connotation
Carries a positive connotation, implying respect for the advice given. 
She left us with a pearl of wisdom about living life to the fullest.