"The hopeless case"

You are a disappointment
of somebody's expectations, maybe.
Did you know them going in, or only find out now?
If you only found out now, consider: you were not supposed
to meet a bar that you did not suppose
yourself no way no how.

Take it with a lick of salt.
A salt lick weighs a ton.
Lick until they go away
or 'til the licking's done.
If they insist, give them a lick. Just drop it on their head.
I mean this metaphorically.
Don't disappoint me, hon. Instead:

Refer to measurements you trust,
and standards set yourself.
Another's hopes are fine by them.
Go hold your own, make all the fuss
you mean to make, for all it helps.

Let no one's hopes - except your own
- come dashing down in rains and pours.

The hopeless case
is one involving

someone else's hopes than yours.