It's been two days of hard work and long hours, but I've finally cracked it.

Twelve hours yesterday, another ten today. An unexpected but critical deadline, the kind where you pull out all the stops and do what has to be done. I upload the final version, I know I've given it my best, and I click submit with real pride.

I am now fully prepared for my lip sync video with the rapper Macklemore.

I may have overcooked this one. In my defence, I'd won the Microsoft Founders Award. One employee a year out of 220,000, and part of the celebration is a lip sync broadcast across the company alongside the real Macklemore, live from his ‘crib’ in Seattle. You also get a watch, engraved on the back by Bill Gates.

Of my 22 hours of blood, sweat and questionable dancing, five seconds made the final cut.

I tell you this because it's the closest I've been to the famous version of business success, and it taught me nothing about how to build one. What taught me was four goes at a side hustle. Two failed. Two made money. Neither of the two that worked looked remotely like a unicorn (yet!).

Because here's what nobody explains about the word profitable. It comes in about three different shapes, and only one of them needs a big idea.

Shape one: the hobby that starts paying

The lowest rung, and the one nearly half the country is already standing on. 46% of UK adults now earn money from a side hustle. Photography at the weekend. Cakes baked in the evenings. Candles sold on Etsy.

The maths here is beautifully simple, which is why it works. Sell handmade candles and your fixed costs are your Etsy fees and a bit of hosting. Your variable costs are wax, wicks and postage. You're profitable on the first candle that covers them, and you can be trading inside a week.

The trap is the word hobby. Until money changes hands, it isn't a business, it's something you enjoy that costs you money. I've watched people spend two years perfecting something lovely and never once ask a stranger to pay for it. Charge from day one, even badly. Getting your price wrong teaches you more in a fortnight than another year of tinkering ever will.

Shape two: sell what you already know

The second shape, and the one I'd point most people in a decent job towards. My first two attempts at a side hustle took three years between them and both failed. My third was a consultancy. It took eight months, and it worked.

It worked because I already owned the product (my knowledge). You've spent 10 or 20 years accumulating something companies pay real money for, and nobody has to build anything. No inventory, no app, barely any fixed costs. You're profitable from your first invoice.

Two warnings. Cash is slower than you think. Two months to win the contract, a month to deliver, then 30 days payment terms, and you've gone four months with no income while the costs carry on regardless. My first successful hustle needed me in London three evenings a week, which was £300 a week in trains and dinners before I'd earned a penny. And you're selling hours, so your ceiling is the hours you have. Fine if you want extra income. A problem if you want out.

Shape three: the business that outgrows you

The third shape earns money when you're not in the room. My fourth attempt was an impact measurement software business. It went from idea to launch in two months and did well enough that I handed in my notice.

It wasn't a stroke of genius. I found a report saying 60% of companies were still measuring this stuff on a spreadsheet, and worked out there were around 8,500 organisations who needed it and already had the budget allocated, all being served badly. That isn't vision. That's reading a report properly and then picking up the phone.

This shape has the highest ceiling and by far the longest wait. If you're building something you eventually want to sell, you'll be lucky to see real money in the first four years. Being an entrepreneur is living like most people can't for a few years, so you can live like most people never will if it all pays off.

Profit doesn't care which shape you pick

Every one of them lives or dies on the same four numbers. What it costs to win a customer. What that customer is worth to you. Your fixed costs. And how many sales it takes to cover them.

In my book I use a made-up business called PawSwap (based on one of my really early business ideas) to show what happens when you skip that bit. It matches dog owners with trusted co-owners for £9.99 a month. Lovely idea. Except the average customer solves the problem in about three months and leaves, so they're worth just under £30. It costs £15 in ads to win them and £6 to serve them, which leaves £9 to throw at £430 of fixed monthly costs. You'd need nearly 50 new paying customers every month just to stand still.

That's the whole reason PawSwap doesn't work. Not vision, not disruption. Arithmetic. And the lovely thing about arithmetic is that Bill Gates has no advantage over you in it.

Pick the shape that fits the life you want

So before you decide you're not the type, work out what you're after.

Want extra income alongside the job? Take the hobby and charge for it. You could start this month. Want to replace your salary? Sell what you already know, and go in with your eyes open about the cash flow. Want something that keeps earning when you're not at your desk? Build the product, and be patient with it.

None of those three needs a billion pound idea, an MBA or a garage in Silicon Valley. They need a customer, a price, and costs you can count on one hand. I left school at 16 and worked all three of them out with a laptop at my kitchen table after the day job.

The watch is lovely, by the way. It lives in a drawer.

You're not going to be the next Bill Gates or Mark Zuckerberg. Neither am I. Turns out you don't need to be.

Jimmy Cockerton is the author of No Risk Side Hustle: BUILD your business in 60 days without quitting your job is out now, published by Pearson.