Anger at yourself, the speaker says, has no obvious outlet. You can argue with another person, but arguing with yourself is considered strange, and nobody offers advice on making peace with your own mind. The refrain "That's the problem" returns like a tired sigh, as if the speaker keeps circling the same dead end.
The central image is a pot of boiling water. Optimistic and pessimistic selves take turns at the handle, swinging the heat from calm to irritated, until the water spills over and the pessimistic voice wins. The damage, the speaker notes, lands only on themselves. The final comparison is the most striking: a doctor who knows how to treat everyone else but can't treat their own illness.
The mood is weary, honest, and a little helpless. The plain, unpolished language makes it feel like a confession rather than a performance, which makes the admission of not knowing what to do feel real.