Sometimes lying is just escape. Escape from life. Escape from pain. "How are you?" "Oh I'm fine." When really one is dying inside.
Sometimes lying is just keeping up appearances. Like "How much did that watch cost?" "Oh, $200" when one really got it at a flea market but doesn't want to look cheap or less successful than friends.
Sometimes lying is to escape punishment. Mom to kid. "Did you eat that cupcake?" Kid "Nope, wasn't me"
Sometimes lying is to gain something like attention or sympathy. "I'm so sick I have the worst cold ever." When one really has a sore throat and a small cough.
Lots of reasons for lying.