We all have ideas. We all have goals. We all have dreams. So why are some people able to turn their dreams into reality, while so many do not?

According to Spanx founder Sara Blakely, the difference comes down to one word.

"The difference between people who achieve their dreams," Blakely recently wrote on Instagram, "and those who don't is simple. It's about ACTION."

According to Blakely, 20 years ago she had no money and no experience. All she had was a crappy job and a crazy idea. 

"I could have easily sat back and continued to say ... 'one day,'" Blakely writes. "I could have kept dreaming, hoping, and wishing. But instead, I started doing, and one day became day one, 20 years ago."

Day One, or One Day?

When you don't act, when you don't start, you can console yourself by thinking that you have no way of knowing how pursuing a dream will turn out.

But not trying, not acting, not finding out how things could turn out? That only leads to regret. 

Every day, would-be entrepreneurs let hesitation and uncertainty stop them from acting on an idea. Fear of the unknown and fear of failure have often stopped me, and may be what sometimes holds you back too.

Think about a few of the ideas you've had, whether for a new business, a new career, or even just a part-time job.

In retrospect, how many of your ideas could have turned out well, especially if you had given the opportunity your best effort? Would a decent percentage have turned out well?

My guess is, probably so -- so try trusting your analysis, your judgment, and even your instincts a little more.

Try acting. 

In Blakely's case, she was in her late 20s when she had the idea for what became Spanx. She kept her full-time job selling office supplies while she bootstrapped the company, working and side-hustling and grinding -- and hearing "no" countless times.

But she stayed the course and became the youngest self-made female billionaire in the world.

As Blakely says, turning "one day" into "day one" made all the difference.

While you may get it wrong some of the time, if you keep thinking "one day ... " you will never have the chance to get it right.