The amount of things you need to learn in biology is truly hard, though from what I've heard, there's nothing harder than quantum physics, since it's so fundamentally different from how we're used to seeing things.
I think that's his point. Your instincts fail you all the time when studying stuff smaller than atoms
Most people don't have a gut feeling for overriding their instincts in favour of math. In fact, when you read some behavioural sciences you'll notice that overriding math with your instincts is the norm