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.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
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.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.