What does they believe that a person's true potential is unknown (and unknowable); that it's impossible to foresee what can be accomplished with years of passion, toil, and training mean?

These people believe that a person's true potential is unknown (and unknowable), that it's impossible to foresee what can be accomplished with years of passion, toil, and training.-People with fixed mindset believe love is ideal, instant, perfect, and characterized by perpetual compatibility. Like it was meant to be. Like "living happily ever after."  

-Unfortunately, people with fixed mindset believe relationship failures and rejection say something about them

Growth Relationship Mindset

-People with growth mindset believe that they, their partner, and their relationship can grow and develop  

-Importantly, growth mindset doesn't mean there isn't a "soul mate" out there for you. It does mean that even with that destined person you will continue to grow and get better!

Explanation:

needs an explanation

i suggest it is anadiplosis