Think of it like daleks being out of sync from doctor who and it explains everything perfectly. It's like a separate existence; not separate in space, but in time. It's just experiencing things a second sooner or later than everything around it. It's not the same as just travelling in time by a second, but when you're in one second, everything else is in the next second. You can't catch up with them because when you reach that next second, everything else is in the one after that.