When I've felt low self-worth, the feeling is the emotional component of my own self-assessment.
In other words, low self-worth is the result of my own assessment of me.
I have assessed myself.
And I have then validated, approved my own assessment of myself.
To have low self-worth, therefore, requires one to have a very high regard for one's capabilities.
If I didn't so highly value my own ability to assess myself, I couldn't think ill of myself.