something that motivates someone; something that makes someone behave in a certain way. (Informal.)
William is sort of strange. I don't know what makes him tick.When you get to know people, you find out what makes them tick.
Idiom
what makes someone tickwhat makes (someone) tick
if you know what makes someone tick, you understand the reasons for their behaviour and personality.
A good salesperson knows what makes a customer tick.
what makes (one) tick
The things that motivate one or make one behave in a certain way. I'd love to sit you down for an interview so I can find out what makes you tick.Janet is a very private person, so it's hard to know what makes her tick.