If you wanna put it in economics terms, it's basically the difference between fixed costs and variable costs. Scalable professions have high fixed costs and low (or no) variable costs. So it may take you 10 years to learn how to program well and 3 years to write a killer application, but then once you've done that, you can sell as many copies as people will buy for zero cost. Naturally, this is high risk & high reward: many people give up before they've built a product that other people will buy.
It gets a little complicated because in a profession that's innately scalable (like computers, writing, or any sort of IP), the distinction between scalable and unscalable business models usually comes down to who's bearing the risk. So, if you're an entrepreneur, you front all of the fixed costs of developing the product yourself (or you get investors to do it in exchange for equity). In return, you get all the rewards if it's successful. However, if you're an employee, you sell your labor for a fixed price (= unscalable, since you have only a fixed amount of time), and then the company bears the risk of the product not succeeding in the market.
Personally, I think you should think of an employer as an insurance company: they underwrite the risk that your venture will fail in the marketplace, in exchange for taking the vast majority of the rewards if it succeeds. Whether or not this is a good tradeoff depends a lot on things like external economic circumstances, your skill level, ideas you have for new markets, etc.
It gets a little complicated because in a profession that's innately scalable (like computers, writing, or any sort of IP), the distinction between scalable and unscalable business models usually comes down to who's bearing the risk. So, if you're an entrepreneur, you front all of the fixed costs of developing the product yourself (or you get investors to do it in exchange for equity). In return, you get all the rewards if it's successful. However, if you're an employee, you sell your labor for a fixed price (= unscalable, since you have only a fixed amount of time), and then the company bears the risk of the product not succeeding in the market.
Personally, I think you should think of an employer as an insurance company: they underwrite the risk that your venture will fail in the marketplace, in exchange for taking the vast majority of the rewards if it succeeds. Whether or not this is a good tradeoff depends a lot on things like external economic circumstances, your skill level, ideas you have for new markets, etc.