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.
See also: make, tick, what

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.
See also: make, somebody, tick, what