Not know (one's) ass from a hole in the ground slang rude
To be extremely stupid; not to be alert
She didn't know her ass from a hole in the ground when quitting such a decent job.
What! You refused such a good price! You don't know your ass from a hole in the ground.
To have no money
Extremely stupid
Very stupid, or silly
Used to describe someone who is naive, gullible, inexperienced, easily fooled, ignorant, unsophisticated, etc.
To say, or believe something or someone that seems completely crazy, delusional, or stupid
The origin of this slang is not clear.
One needs to understand the basic techniques or primary details of something before taking actions that require greater skills
Peter failed because he did not learn to walk before he ran.