Plenty of articles exist detailing how to build a successful startup, but little has been written defining “success.” After years of hard work, many business leaders still feel they haven’t yet made it, mainly because there always seems to be someone making more money and winning more awards.

For many business owners, the realization that their startup is a full-fledged business comes suddenly, as a result of some event. That “aha moment” can make a big difference in a business owner’s confidence and peace of mind. But how do you know when you’ve reached that point? There are several telltale signs that you’re doing something that’s resonating with customers and you've made it, or about to make it.

Follow the metrics.

Each day, consumers create 2.5 quintillion bytes of data. The tech community is only now learning how to harness all of that data to gain real insight into customer preferences. With so many metrics available, startups can watch their company grow, day after day, one transaction at a time.

For Eventbrite’s Julia Hartz, it was that very type of data insight that allowed her to watch her company grow. In 2009, the company saw the growth of the number of self-made entrepreneurs using Eventbrite reach phenomenal numbers. As data science becomes even more sophisticated, businesses will be able to chart their growth and determine a point at which customer usage numbers reach all new levels.

When Greg Hayman, founder of SEO.io, launched his startup several months ago, I talked with him about what makes a business succeed. He told me "knowing every detail of your business will determine it's success or failure. You must know every metric that makes your business successful and cut the metrics that aren't delivering success."

Related: Success Lessons From 2 Innovators Who Came Out Swinging

Longevity.

One of the best tests of success is time. Since an estimated 49 percent of businesses fail within the first five years, it stands to reason that if a business is still in existence after that five-year mark, it’s likely doing something right.

When I started Due it took me months before I started seeing progress but I held fast to my goal to build something meant to last. I was taught this by David Semerad from STRV, one of the best development companies I've ever worked with. David told me, "We work with so many companies that struggle with what it means to be successful. Wondering when they can come up for air. The challenge is that no matter how big you get there’s always a risk to success. It really is an ultra marathon and you just need to keep moving, listening to your body (your customers) along the way."

Build your startup for longterm success.

Related: The Secret Sauce of Successful Entrepreneurs? It's All in Their Head.

Listen to your peers.

When former recruiter Perri Gorman founded Archively, she had already rolled out an email unsubscribing service called Unroll.me. But her background in hiring inspired her to pour her energies into her new, intelligent recruiting app. When a peer told her that her application was bigger than even she realized, she began to realize her app had a value beyond the basic workflow she’d created.

In addition to the many other benefits peer networks provide, they can be invaluable for serving as a progress check. Fellow entrepreneurs can offer objective insights into how your business is doing, as well as tips for improving. Often you’ll find that a peer sees the signs you’re successful long before it ever occurs to you.

Listen to your customers.

SurveyMonkey's former CEO Dave Goldberg, who passed away recently, had perhaps the best advice for how to recognize when a brand is succeeding.

“I think when you get people telling you that it’s really significantly changed their behavior in a permanent way,” Goldberg said. “Something that’s good enough to open people’s eyes to the behavior they had before and this changed behavior and that it’s repeatable and they like it enough that they’re not going to go back.”

Dave was an inspiration to me over the years. He ran one of the finest companies out there and his customers loved him. I will miss his knowledge.

In an era when customers take to social media to report a bad customer service experience, it’s more important than ever that brands be proactive in gauging customer attitudes. Brands must open a line of communication with their customers and look for changes that signal their products or services are, or are not, truly resonating with customers.

As hard as entrepreneurs work to build their startups, it can seem anticlimactic when they finally reach full-fledged business status.

While balloons may not drop from the ceiling, chances are you’ll have a moment when you realize you’ve created something that is getting a response from the marketplace. When that moment comes, take a moment to celebrate before rushing toward your next milestone.

Related: Dave Goldberg, Entrepreneur and Husband of Sheryl Sandberg, Dies at 47