Your teeth can shift back if you stop wearing your retainer.
It's important to keep wearing your retainer for as long as your dentist says you should.
Though the process becomes slower and slower, if you stop wearing your retainer, your teeth will gradually move back to their original position. In a way, teeth remember their original position.
If you don't wear your retainer, your teeth will eventually shift back to their old positions.
This is particularly true in the months and even years directly following treatment with aligners or braces.