Lids are useful.
Lids are the things you put on boxes or jars to keep the contents in, safe, fresh or dry.
Eye lids are the part you close to cover up your eyes.
But as an idiom, keeping the lid on something is about keeping something from coming out into the open or into the public domain.
The government sold weapons to Iraq but they kept the lid on it.
Here's a guy who doesn't know how they keep the lid on a hallucinatory drug called DMT. He just doesn't know how - probably because he's stoned is my guess!