I know I'm forgetting something
When your brain is trying to tell you you’re missing something, but you’re too lazy to figure out what it is, and you just hope it doesn’t matter.
He was at the gym and thought, 'You forgot your towel!' He went home and came back with a towel, but then he forgot his shirt.
She was at the airport and thought, 'You forgot your phone!' She ran back home, got her phone, and realized she forgot her keys.
He was about to go on a trip and thought, 'You forgot your luggage!' He had to run back home and realized he forgot his clothes.