Why do 40-50 percent of teachers quit within the first five years?

Why do teachers have one of the highest fail/quit rates among other career professionals?

I remember discovering this when I was sixteen, and we had to write about the career path that we wanted to follow. That was fourteen years ago, and I am now trying to land my first full-time gig as a teacher.

It hit me hard because I feel I will be one of the stats.