I think the pro maybe talking about a continuation bet, for the size of the bet.
A continuation bet is a bluff that you could use if you were the agresor preflop and only one person called. Then before the flop he checked to you and even if you don't hit nothing on the flop you can make a bet around half the pot in an atempt to take it.
This situation is profitable because if you're only against one opponent the chances that the flop hit is hand are about 33%. So you're investing for example $500 to win $100 in a situation that you're opponent may fold about %66 of the time.
I think this although it applies to all bluffs not just cbets. Say you're on the button with trash and raise to 3x to steal the blinds. You're risking 3 to win 1.5 and thus must win 2/3 of the time to break-even (ignoring meta-game and the fact that if you raise trash from the button you'll get more from your big
hands and the fact that you could hit a hand or win the pot on a later street).
Basically this relates to Fold
equity in a bigger sense. Especially when you have a strong draw, when you bet you will take down the pot right there to give you some equity in the pot and when called you'll have some % to win. I won't go in to calculations but that's the basics of it.