what makes somebody 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.
what makes somebody ˈtick(informal) what makes somebody behave or think in the way they do: I’ve never really understood what makes her tick. ♢ Money is what makes him tick.
Tick here is the sound a watch or clock makes as the hands move forward every second.