Sometimes, you have cards that demand an impossible decision.
I'm dealing. I've got a 344455 hand.
There's any number of ways of keeping 8 points. I could keep either a 3445 or a 3455.
A 5 in the crib -- when it's my crib -- isn't a bad thing. But. It seems better to keep the 5's together. The possibility of 10-point card as the starter is a $\frac{4}{13} = 30.8\%$ possibility.
I decide to drop a pair of 4's into my crib. The outcome?
Two 15's and a double-double-run. 20 points. Plus a few points in the crib. Well above par.