When you a programmer you can work for a while, finish your code, have it pass tests, and then you are done - with 100% confidence that your work resulted in the outcome you sought (code that works).

When you are product/marketing/sales person, you typically work for a while, aren't sure if what you are doing is correct or optimal, maybe find out later it did or didn't work, and then you have to do it again and again and again.

So, to make the transition, you have to get comfortable with the uncertainty inherent in business activities. To put it another way: You'll "fail" far more frequently in business than in programming, and the causes of your failure will be far less obvious.