Jokes aside, this is what I love about humanity, and the thing I believe defines us as human: the capacity for growth and change.
We had thought them hopeless, but Reed was able to change his mindset and grow as a person.
I truly believe that, given enough time, humans are capable of anything, and both Reed and Iren are proof of that. Iren started using the magic he had grown up with, but switched to human casting to fit in. He then went to the natural next step of that: adding his own knowledge into the casting to change it. That's how an incomplete chant for light became castable and reproducible. Humans have unlocked light magic.
To grow and to change is to be alive.