Happened to me a lot.
For instance, when sleeping, sometimes I forgot that I didn't put on diapers so I wet the bed. Or awoken in the middle of the night only to remember that I wear them so I just wet them half-asleep.
It doesn't only happen at night, sometimes I thought I was wearing diaper so I just let go, half-wetting my pants before I realised. Or holding bladder for a while before realising I was wearing diaper.
Getting too used too diapers is dangerous.