A number of years ago when I was a number of years younger, I worked with a particularly challenging student. It seemed that it didn’t matter how many different ways I tried to explain a concept, she didn’t get it. If she did understand something, it seemed she forgot it the next day. I thought there would be no way she would pass a course.
But this particular challenging student who I worked with a number of years ago when I was a number years younger surprised me. She worked hard. She persisted. If she did poorly on a test, she worked harder. If she did well on a test, she worked harder. She persevered. Not only did she pass a course, she completed an entire college program.
I had misjudged her. I made the mistake of believing her abilities were fixed and that no amount of effort would help.
Whereas I had a fixed mindset, my student had a growth mindset.

In her book Mindset, Carol S. Dweck writes:
This growth mindset is based on the belief that your basic qualities are things you can cultivate through your efforts, your strategies, and help from others. Although people may differ in every which way—in their initial talents and aptitudes, interests, or temperaments—everyone can change and grow through application and experience.
This growth mindset is something I’d like to have. But it’s not something one has; it’s not a possession. Instead, I believe a growth mindset is something you constantly work towards. And I’m grateful that a particular challenging student in my past helped me realize this.