The speaker feels misunderstood. People see the smile and the tear, the surface of things, but not the anger or fear underneath. Even when something small goes wrong, like spilt milk, or something sadder, like a dead fish, others ask if they're alright, as though a simple question could reach what's really going on.
The offers of help are kind: a hand, a shoulder to lean on. But the speaker says they don't want them, because the person offering doesn't realise that what's needed is for someone to understand how they truly feel. The closing image makes the point neatly. Walking a mile in size 8 flip-flops while the other person has size 9 feet suggests that nobody can fully stand in another's shoes. Well-meant comfort ends up not fitting.
The mood is quiet, a little weary and lonely. The short lines and plain wording keep it restrained, so the frustration comes through gently rather than as an outburst, and the speaker seems to be hiding more than they show.