I'm still scarred by an interview I had for an investment firm when I had my first wobble about clinical medicine. They had figured it might be cheaper/easier to hire doctors and train them on investment then teaching people with a business background how to understand biotech/pharma innovations.
Massive room in swanky Mayfair office, with a single glass of water on it. Tosser in expensive suits looks me in the eye and says "If I pick up this glass of water, drink half of it, then hand it to you and you drink half of what's left, and we keep doing this until all the water has gone... how much will each of us have drank?" I got lost in world of mentally adding up ever decreasing fractions and ended up stuttering nonsense. Still pisses me off to this day that I couldn't instantly come up with the answer.