Reflection.

Phillips, The Angler, 1926

Student reflection is a key ingredient in project-based learning, and for good reason. As John Dewey reminded us nearly a century ago, "We do not learn from experience . . . we learn from reflecting on experience."

Reflection not only makes learning stick at the end of a project but also helps students think about what's working well and what's not during Problem-Based Learning. When students take time to reflect on their progress, they can make revisions or course corrections so that they can achieve better results. 

The same holds true for teachers.

... or anyone. Read the rest at Edutopia.