I was 'weeded' out of pre-med and landed in software. The problem with pre-med was the insane number of hours per semester I was going to have to take while I was also working. I had an interest in computers so tried out the first programming classes and it was relatively easy so the rest is history.

IIRC, for software/programming, any early class heavy with pointers/hardware/math served as a weeding function. So I'm not sure how students won't be pushed out at some point if they can't do the work.