This expresses pretty much what I was going to say. To contextualize it a bit, I always mentor people to start by getting a job in a company that is doing something in their skill set. Instead of looking at it as "just a paycheck until I can start my own thing." try to actively learn about how that company works, really works, from marketing to sales to manufacturing to legal to operations. Most people are willing to mentor if you tell them that you are hoping to start your own company one day and want to know what you don't know.

Ask questions of people like product managers of the form, "How do you validate your ideas for products before you commit to invest building them?" or "What product did you think would be a hit and was a total flop? What caused it to flop?" Ask people in release engineering or manufacturing, "What takes the most time in getting a product out? How about a feature to a product?"

If you are a software developer, imagine that a functioning, growing company is a large legacy code base that you want to learn how it works. How the pieces work together, what the roles of the parts are. If you're a hardware engineer imagine the company is a big circuit you're analyzing, same thing, what do the parts do and how do they contribute to the overall functioning.

You will get to know a lot of people in the company and you will get a much better understanding of what it takes to bring a product to market.

What ever you do, and this applies to people anywhere in their career, do NOT consider any job "just a paycheck." Use a job to learn more about why people are willing to give this company money so that the company can pay you to work there.

The secret, such as it is for entrepreneurs, is "For what reason would people give me money?" And you can also ask "What would I pay for this idea?" and then subtract from that what you've learned from your work experiences would be the costs of producing it.

PS> Even the best university education does not train you to build a successful company from the ground up. Nobody teaches that, you have to learn it from people who have done it or even better are doing it.