For some people the possibility of prison may deter those people from criminal behavior.
Even for some people the thought and possibility of being locked up in jail is enough to deter some people from doing any crime.
However not every is deterred from crime or criminal behavior just because they will or may wind up in prison.
Some people who have been to jail or prison commit more crimes and then go back to prison or jail and it doesn't seem to phase them or deter them from committing any criminal behavior.
Prison doesn't actually deter much crime and doesn't really rehabilitate many people from crime and sometimes being in prison makes the person a better criminal because they are around other criminals.
They can also do bad things in prison because they have nothing but time on their hands to do things.