It's a sad truth that most of us never end up reaching our "full" potential. We have business ideas that we never follow through with, or we end up complacent at some point in our careers. While there's no real gauge for maximum potential, most of us know innately that we haven't yet done everything we could have possibly done.

Why is this? There are several reasons, but almost all of them are mental, and that makes them possible to overcome in almost any circumstance.

The secret to overcoming these mental hurdles is accepting certain truths about success and your potential. These nine realizations are important--maybe even necessary--if you want to achieve everything you can possibly achieve:

1. There's never a perfect time.

Many of us delude ourselves by suggesting that now isn't the "right time" to start pursuing our goals. It isn't the right time to ask for a raise because the company isn't doing exceedingly well, or it isn't the right time to start a business because you don't have your idea fully fleshed out. The problem is, even once these obstacles are cleared, new obstacles will arise to take their place. There will always be reasons not to do something, and it will never be the "perfect" time. Knowing that is key if you ever want to initiate anything.

2. Effort doesn't always pay off.

The fairy tale version of success goes that if you try hard enough, and put enough work in, you'll be successful. Unfortunately, this isn't always the case. Sometimes, you'll work very, very hard, but you won't get anywhere, because your idea was weak or your timing was off or because some other circumstances prevented you from making progress. Knowing this can help you prepare for those inevitable failures, and prevent you from becoming disillusioned when they actually occur.

3. But effort is always worth it.

Even though effort doesn't always pay off, effort is always worth it. In failure, you'll learn what not to do in your second attempt. In poor timing, you'll gain experience and improve skills you can use elsewhere in your career or business development. Even if you waste your time completely, you'll at least get a better sense for what is and what isn't a "waste of time," and you'll work more productively in the future.

4. High expectations are rarely rewarding.

High expectations are exciting; you'll push yourself harder, you'll fantasize about the possibilities of your efforts, and you'll be more excited about what you're doing. Unfortunately, too high expectations rarely result in good long-term results. You won't hit your overly optimistic targets, and things won't go the way you planned, leaving you resentful and compromising your plans. Instead, hope for the best and prepare for the worst--expect to see conservative returns, and try not to overestimate your propensity for success.

5. "Busy" and "productive" are not synonyms.

Just because you're occupied doesn't mean you're making a valuable effort. It's easy to keep yourself busy with tasks, but if those tasks aren't leading you to any higher goal, they aren't doing much good for you. Learn to distinguish between productive work and busy work, and you'll end up getting far more done in a shorter amount of time.

6. You will never be the best.

No matter how good you are at anything, there will always be someone better than you. Even if your business rises to become the dominant competitor in a given market, at least one competitor will be able to outdo you in at least one area. This isn't a bad thing; in fact, it can be a good thing. Once you realize this, you can stop focusing on trying to outdo everybody else and start focusing on what makes you unique from them. Trying hard to be the best will only muddle your goals and leave you frustrated.

7. Inaction is more regrettable than action.

Generally speaking, people tend to regret the things they haven't done more than the things they have done, even if the things they have done were particularly regrettable. This information is useful when you're facing a risky or scary decision--even if you follow through and fail, you'll regret it less than if you never tried it at all.

8. Everyone has something to teach you.

This is a key lesson for personal development, but it's one some people never realize. Everyone in the world is better than you at something, and knows something more than you do. If you take the time to talk with people, whether they're mentors, coworkers, or even stranger son the street, and truly listen, you'll walk away with a wealth of more knowledge and second-hand experience.

9. Success may not be what you thought it was.

This is also important to remember. Many people go their whole lives chasing wealth, or fame, or some other conventional measure of success. But when they get to that point, they realize it's not making them happy, or that it's not what they really wanted in the first place. Other people find out halfway through a chosen career path that it isn't for them, or start a business to find it more stressful than satisfying. Be prepared to have your assumptions and expectations challenged. Success is out there, waiting for you--but it might not be in the form you expected.

Once you accept these nine fundamental truths about success, work, and development, you'll be far more flexible, more persistent, and mentally tough enough to achieve whatever goals you set for yourself. It may not seem like they make a big difference, but as soon as you accept them as reality--rather than just reading them on a page--you'll feel it for yourself.