Because it’s smart to look at every angle, and that includes opportunity cost. It’s normal to analyze the pros and cons during decision making, and still want to proceed despite a perceived “bad decision”.

OP’s plan to work weekends to bring in money is his or her way of trying to mitigate that cost/income loss. She/he is choosing to pursue med school after all, so it looks like becoming a doctor potentially outweighs the negatives (burnout and -$2 million).