We Grew a Company From 12 to 150 Employees in 4 Years. Here's What We Did Wrong. These are the four mistakes fast-growing companies typically make.

Growing a business of any kind is a crazy ride. It's fun and challenging and scary. I know because I was part of a team that did it. Our company grew from 12 employees to 150 in just four years. And that's great.

But, mistakes? We've made a few. OK, we've made a lot.

Don't get me wrong: A certain amount of hubris was driving us. Although a recent study said CEO hubris can be harmful to a company, it's natural -- and even necessary -- to pursue those big dreams and think about what you can do rather than what you can't.

Related: 5 Signs That You're Overworking Your Employees

Still, mistakes are inevitable, and we've had to course-correct many times.

As the year wraps up, here's a look at the mistakes we've made over the past few years and the improvements our team has made as a result. My purpose is to help other founders see those same bumps in the road before they themselves encounter them and to learn from some of our hard knocks.

1. Don't abuse people's commitment.

The "dark days" were in 2015. Because of our desire to stay on top financially, we worked people way too hard, and almost lost some of our best people. We demanded 10-plus-hour workdays of everyone, with no end in sight. Morale crumbled, and no one wanted to work with us.

You might think this is a given in startups, but it doesn't have to be. Caring for your people is a better strategy for the long-term health of everyone (and of your business).

Amazon has a reputation for having a demanding, fast-paced culture. Although no one can argue with the company's phenomenal success -- just look at the fierce competition that cities and states waged when trying to land the company's second headquarters -- it's not for everyone. The median tenure there is just one year.

No matter how bad you "want it," be mindful that there's a limit to what most of your team members are willing to stomach. Small bits of gratitude go a long way.

2. Don't confuse strong contributors with leaders.

In the next phase of growth in 2016, we had to learn about developing leaders. Good individual contributors are not inherently good managers. In fact, they are rarely good leaders.

We weren't alone in this mistake. In an HBR-reported study of business leadership, 61 percent of executives surveyed said they weren't prepared for the challenges they would face as leaders.

Clearly, then, developing leaders is important, even though it's a time-intensive project. Our strategy? We learned to pick people we like and to spend a lot of time with them. A lot. This can't be overstated. Only by focusing on your investment in potential leaders can you expect those people to learn to lead your company.

3. Don't delegate culture and training too soon.

Assume you will always be the culture driver of your company. In 2017, we made the mistake of delegating our culture to others. We thought the 20 people who loved our culture and were ambassadors for it would ensure the next 80 were on the same page.

But they weren't. Culture and training are the most important jobs of an entrepreneur. No one carries as much weight as you do, and it's vital that you be the articulator of your culture and values.

So, don't delegate the job too soon, if ever. The telephone game is real, and messages get changed as they are passed along from leadership to management, as well as from one employee to the next. Insights and nuance also decay as time passes. Your 150th hire will never be as clued in as your first unless you make that a priority.

Warby Parker makes training a primary focus, even among senior staffers. Our co-founder Dave Gilboa says that it's important for new employees to feel welcome and for senior staff to help guide them on a successful path from the beginning.

Related: Six Ways to Create and Build a Successful Company Culture

4. Don't emphasize comfort over productivity.

In 2017 and 2018, we made a lot of mistakes. The good news is that we learned from our mistakes of 2015 (overworking our people). The bad news is that we swung too far the other way. We spent a lot of time, money and energy on comfort. Now, my partner and I suffer from "Chris Rock syndrome": As the comedian puts it, "My kids are rich -- I have nothing in common with them!"

We overdid it by acquiring a great working space, snacks and other luxuries. We trained our employees to feel entitled to creature comforts instead of keeping that "stay hungry" mentality startups have. Overall, this isn't a bad problem to have, but dialing it down could be good for the organization.

Like parents' view of their kids, we didn't, we don't, want life to be hard for our people, so we try to treat them well because of the struggles we went through.

Related: The Perfect Work Environment Has To Be One That Does Not Feel Like, Well, Work

Still, if you start adjusting the course of your business to meet the demands of every employee, you will lose direction and focus. So, absolutely pay attention to what your team needs in order to be successful, but also be sure to distinguish perceived issues from real ones.

As an entrepreneur, you're going to make mistakes. But, as you prep for 2019, think through the mistakes we've made and do everything you can to avoid them.