I tend to think of this concept when I hear people say that they "can't make the student do their work." Imagine the student's motivation like a teeter-totter. On one side you have a bucket of how they feel about themselves and on the other you have a bucket of how they think people feel about them. As instructor's we can't fill the first bucket, but we can fill the second bucket with enough praise that it tilts the seesaw and you dislodge the student from feeling like they're stuck in the mud.