Back when my startup was going through its initial growth stage, I reached out to a lot of founders for advice.

All of them shared little pieces of wisdom that had worked really well for their companies. Our team was still at the point of trying to figure out product-market fit, so I was thrilled to get insights from entrepreneurs who knew what they were talking about.

But every time we tried to implement the advice, it just wouldn't work.

After a while, I realized we had to create our own path. There is no magic pill or secret formula that will make your company successful. Instead, it's a constant process of testing, identifying what works, and moving forward. Over and over again.

Here are a few things I've learned since then about building a company from scratch:

You have to identify a massive opportunity and capitalize on it.

There is one piece of advice I've held onto over the years: whatever you're attempting must impact a large number of people.

With ThirdLove, the initial research showed the intimate apparel market was huge--about $16 billion in the U.S. alone. This makes sense when you stop and think about it. Almost every woman wears a bra, meaning the market encompasses roughly half the population.

As big as this market was, we found the online bra market was underdeveloped. That was our opportunity to give women a new way of thinking about how they buy a bra and find their perfect fit.

Typically, successful companies make good use of situations like this. They introduce a new market or present an entirely new way of thinking about a product or experience. They create their own opportunity through innovation or by changing the status quo.

But understanding the opportunity and capitalizing on it are two different things.

You have to execute on the most basic elements.

Everyone has a vision for their business, but executing on that vision is where most companies fail.

They flounder on very basic elements, like pricing or manufacturing, rather than on more technical aspects of the business. And a lot of companies flop on the most basic element: product-market fit.

A recent analysis of startup postmortems found that 42 percent of defunct startups failed because there was no market need. These companies weren't solving a problem large enough to target with a scalable solution.

Maybe that seems like an obvious flaw when presented here, but the basics can trip up just about any new company.

There was a time when we almost went out of business just trying to find a manufacturer who could make our product. We started out with one manufacturer, but it quickly became evident the quality just wasn't there. We had to walk away and find another manufacturer, and the fiasco ended up costing us $400,000.

It was a very tough situation. We had plans for a great product, and the market was there, but we would have flopped if we had failed to get it manufactured.

The process of building a company is filled with both simple and complex challenges. After surmounting each hurdle, another one arises. Regardless of which basic element you're implementing, each step involves a great deal of trial and error.

You can't expect to find the perfect playbook.

A lot of entrepreneurs ask me for advice about how we got to this point. I'm always happy to share what I've learned and what worked for us.

But I also tell them what I had to learn the hard way when starting out--there is no secret formula.

Every business is unique, and so is each moment in time. The advice I give today will probably be outdated in a year or even less. The landscape will be different in so many ways. And that's why it's so important to keep an open mind and continue to test what works for you.

No matter what, people will promise you the world when you're starting a company.

Some vendors claim to be experts, telling you with overwhelming confidence that they've scaled similar companies and know exactly how to make you successful. But once you work with them, you may find out they over-promised.

The best vendors, the ones you want to work with, will be realistic and upfront. They'll admit the process will be challenging, and they won't promise success. You want to work with people who won't try to sell you a playbook. Because the truth is, there isn't one.