Has anyone had their front teeth move again after finishing orthodontic treatment?

An acquaintance who had braces a few years ago said that their front teeth looked a little different while looking at a photo.

If I don't wear the retainer properly, could changes actually occur?

I thought it would be over once the orthodontic treatment was finished, but I was surprised to find there was more talk about maintenance than I expected.

For those of you with orthodontic experience, how long did you use your retainer?