“I’ll have the proposal to you by end of the day next Friday,” I said as I left my first business-to-business sales meeting. I was 19 years old and about to learn a lesson that would be the key to my new web agency’s growth.

“OK, perfect. Our other bids will be in by Friday, too. We’ll give you a call next week to let you know which way we go,” my potential client replied, smiling.

Let me know!? I thought I had this one in the bag!

But I didn’t have it in the bag. I had a shot at the business, just like everyone else that this company had talked with about their upcoming website redesign. As I walked from the prospect’s office to my car, the confidence I had felt in the meeting came pouring out in the parking lot like air spitting out of a balloon.

I was already working two other jobs to earn enough to pay for my summer b-school classes. But I needed this business to work. In my mind, this was my only ticket out.

The next few days, I tossed around proposal ideas. This was done mostly with myself, since I was a solo-preneur at the time. I needed to figure out what could really blow this prospect away and win their business (and my first client). But ultimately, I got frustrated and just used the template proposal I had already created.

I sheepishly hit send with my attached proposal before heading to my Friday afternoon classes. Defeated and deflated, I attempted to drown my disappointment with whatever horrible college beer special they had at Kilroy’s that weekend.

The weekend came and went and I got a call Monday afternoon that would change my perspective on sales and business forever.

When I picked up that phone, I didn’t know at the time that I was talking to my very first client. I had won the business!

My curiosity compelled me to ask why they had chosen my company for the website redesign. I wanted to know if this miraculous outcome was something I could repeat. And this is what they said:

“Well, you were the only company who actually turned in their proposal last week.”

I couldn’t believe it. All of the other agencies had either asked for an extension or simply not sent their proposal in on time.

Shaking. My. Head.

And here lies the core business lesson: Do what you say you’re going to do.

The more sales meetings I took, the more I realized that there was an epidemic of not following through. And it wasn’t just the web design and development industry, lack of follow through is something that plagues many startups in many industries and prevents them from becoming real businesses.

As I grew my first agency, we focused in on alleviating this pain point and differentiated ourselves by–you guessed it–doing what we said we would do. It became our rallying cry (and tagline):

“Quality design. On time. Guaranteed.”

(Not revolutionary or deserving of a Clio award, but it got the point across and became the driving force behind the early growth of the business).

Since then, I’ve learned that follow through isn’t just a tool to close more sales. It’s a way to build a culture of accountability at your company. It builds trust within your team and a camaraderie that consistently catalyzes growth.

So, do whatever it takes. Give yourself a deadline with a buffer. Plan your time. Hell, skip out on sleep if you have to.

Do what you say you’re going to do.

You’ll close more sales and build better relationships. In the meantime, you’ll build a reputation and body of work that can’t be denied. And that gives you something that’s invaluable in any venture. It’s something I’m looking forward to sharing with you…

So, I’ll have it to you by next Friday.

This post is part of a series, including The Most Valuable Sales Lesson I Learned Selling Vacuum Cleaners Door To Door. Keep an eye out for next Thursday’s post and drop a comment below to share your own lessons learned along the way.