Zoom all the way in. Not the year, not the month — one unit: one customer, one job, one subscription, one widget. Unit economics asks the only question that survives the zoom: when we sell one more, are we richer or poorer, and by how much? Every big financial outcome your business will ever have is that answer, multiplied.
The P&L can't tell you this — it averages everything together. Unit economics un-averages it.
The unit is whatever you naturally sell one more of: a detailing job, a monthly client, a t-shirt, an app subscription. Pick the one your growth actually multiplies.
Number one: what one unit brings in. Real collected price — after the discount you actually gave, after the refund rate you actually run.
Number two: what one unit costs to deliver. The true marginal cost of serving it: materials, direct labor hours (priced at what you pay, including yourself for the hours you personally work in delivery), payment processing, shipping, per-client software seats. This is COGS thinking applied per-unit — if the sale doesn't happen, the cost doesn't happen.
The difference is your per-unit gross profit (formally, the contribution margin — next lesson goes deep). Say a mobile-detailing job sells at $200: supplies $15, three labor hours at $25 = $75, processing ~$6. Per-unit gross profit: $200 − $96 = $104 per job. That's the number the whole business runs on.
Your overhead is a countdown. With a $104 unit and a $6,000/month nut, the first ~58 jobs of the month pay for the company's existence; profit begins at job 59. That's break-even thinking, and once you see the month this way you never unsee it.
Your growth spend has a ceiling. If one more customer nets $104, then spending ads/commissions/referral fees anywhere near $104 to acquire a one-time customer is running in place. Acquisition cost gets its own lesson, but its ruler is forged here.
Some sales make you poorer. A negative unit — price below true delivery cost — means every "win" digs the hole deeper, and hustling harder digs faster. This sounds impossible to fall into; in practice it's common, because owners omit their own labor or forget processing/shipping/rework when they price. If your unit math needs your labor at $0 to look good, you don't have a business yet, you have a job with extra steps that pays you to lose.
Different offerings are different businesses. Run the math per offering and you'll find a $104 unit sitting next to a $12 unit you sell with equal effort. That table reorganizes your marketing, your calendar, and eventually your menu.