My first year in college (a very long time ago...!), I came home for the Thanksgiving Holiday and learned that my younger brother, Chip, was struggling with Trigonometry. Chip was pretty smart, so I was a bit puzzled as to why he would be having trouble.
I sat down with him, and within about 15 minutes I discovered that he had missed one key concept early in the school year, and had been confused ever since. Once I explained that to him, the light went on in his head, and everything fell into place for him.
I was horrified that a bright, promising student like my brother would be left to flounder because his teacher did not have the time to sit down with him for just 15 minutes to figure out why he was struggling. But the truth was (and still is) that many teachers are very overloaded, and really can't devote extra time to individual students. A typical high school math teacher may have four or more classes with 35+ students in each class, so well over 100 students. And with teaching and grading homework, quizzes, and tests, that is a very heavy workload.
It was then that I made the decision to become a volunteer tutor in the Boston public school system (through an organization back then that was called "School Volunteers for Boston"). It became almost a Crusade for me to understand what students were confused about and help them get over those little rough patches that can permanently derail their math studies or make them believe they can't do math. Often times, as with Chip, they may have just missed (or gotten confused about) one simple key concept, and that can be enough to totally sideline them.
Over the many years since then, tutoring has been one of the most rewarding things I have ever done in my life. It is just such a wonderful feeling to see that "light" go on in a student's head and see their joy when they "get it" and realize that they *can* do math.