Without a thorough understanding of how to create profit in a business from the get-go, you’re screwed. You need to be able to subtract profit, taxes, and marketing or sales commissions and still have enough money left over to pay someone a reasonable wage for the hours required to fulfill on that sales. Additionally, you need some left over to cover your overhead (including rent, electrics, supplies, software, etc).
Profit First goes deep on explaining why & how. Get it!