My friend Bob Basil once wrote "My weaknesses define me." He said he wouldn't have a superpower, because he felt pleasure in his weaknesses, if I am remembering correctly. Without disagreeing in the slightest with this brilliant insight, I would like to offer the following twist.
We all have traits that define us, and to call some of these strengths and others weaknesses seems arbitrary. We can name the same trait with a positive spin or a negative one, like stubbornness and persistence, or dedication and fanaticism. Discipline might be the opposite of flexibility; either could be strength or weakness depending on the context. There is no way of determining what a strength or a weakness is outside of particular contexts of judgment.
So if I want you to be flexible, not rigid and unwavering, in your dealings with me, I see your rigidity as defect. If I want you to hold the line with someone else, though, your unwavering dedication is a strength.