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.
make someone or something tick
Fig. to cause someone or something to run or function. (Usually with what. Tick refers to a watch or clock.) I don't know what makes it tick. What makes John tick? I just don't understand him. I took apart the radio to find out what made it tick.