How to measure impact?

If my impossible goal is to impact a certain number of people within a certain amount of time, I’m wondering how I can measure that. I’ve heard you say that for coach entrepreneurs, the only measurement that matters is the dollar amount you’ve brought in. That that has to be the measure of business success. Is this because it’s the most quantifiable measurement of impact? As in, if you are creating real value for other people then that should be something you are able to receive back financially, if that’s your goal?