>In 2011, 43,919 students applied to medical schools. However, only 20,176 of those applicants were accepted into at least one medical school. In other words, 54% of applicants got rejected to every medical school they applied to.
Even if we remove the bottom 10% or even 20% of un-accepted individuals (who we might assume, unfairly or not, are not cut out to be doctors) an absolutely significant number of people would enter the field.