The distinction, from Carol Dweck's research, is between treating ability as fixed and treating it as developable. The difference shows up under failure. A fixed view reads a drawdown as evidence about what you are; a growth view reads it as evidence about what you have not learned yet.
In trading the practical difference is whether you review losing trades. People who experience losses as verdicts avoid looking at them, which removes the only feedback available. People who experience them as data go through them line by line.
Be careful with the cheerful version of this idea. Growth mindset does not mean any strategy will work with enough effort; it means your response to failure is itself a skill, and effort should be aimed at things that give feedback.
Related: fixed-mindset, deliberate-practice, self-efficacy, post-trade-review