what 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.

• a pink slip
• a pipe dream
• a piss-artist
• a piss-take
• a piss-up
• a pitched battle
• a pit stop
• a place in the sun
• a plain Jane
• a play on words
• a poacher turned gamekeeper
• a poisoned chalice
• a poison-pen letter
• a political football
• a poor man's
• a poor man's someone
• a poor man's something
• a poor relation
• a port of call
• a powder keg
• apple of eye
• apple of someone's eye
• apple of your eye
• apples and oranges
• a pretty kettle of fish