When you are running a business alone, you are wearing many hats: you are the product manager, the accountant, the media buyer, the CEO, the CTO, etc..
Guess who the most important person in your business is? That's you. You should always protect yourself by paying yourself first and investing in yourself first.
In fact, I believe every business should serve the entrepreneur - NOT the other way around.
Don't get me wrong, I still like to under-promise and over-deliver to my customers, specifically by front-loading a lot of the work