<p>It takes a certain set of skills and aptitude to be good in Engineering classes, which people soon find out in the "weedout classes" like physics. Calculus is pretty easy for engineers, so that's usually not the reason people drop out, although you should be very comfortable with math. For example, the failure rate of Physics I for Engineers at UIUC was 20%, so right away that's a bunch of people who probably drop the Engineering major (or try again and get an F later on, etc). The fact that weak students drop out along the way also makes the curve harder and harder as you advance.</p>