What you achieve in life is directly proportional to the thoughts you allow to roll around in your mind. And know this: You are in control of your mental content. In fact, the most successful people understand their thoughts are not necessarily true and completely malleable. If that's the case, it makes sense to optimize your thinking for success. Here are a few mental habits you should eradicate if you want to reach your highest potential.

1. Complaining.

Negative thinking is a habit your brain naturally wants to perpetuate. It's because the distance between synapses carrying similar messages--positive or negative--shortens to make it easier for information to be shared via brain circuitry. In other words, thinking a thought makes it easier to think it again. Essentially, negativity is a habit that can skew your personality to be perpetually gloomy

2. Believing yourself to be an imposter.

A vast majority of high-achieving individuals suffer from this harmful thinking at one time or another. In spite of their diligence and hard work, these people harbor a fear of being exposed as a fraud. Their success--they secretly believe--is due to luck or other factors unrelated to their intelligence or skill. If this is you, stop. Not only is this a form of maladaptive perfectionism, researchers have found that people who exhibit this "imposter syndrome" tend to have lower levels of job satisfaction and organizational citizenship behavior, which is a person's desire to perform beyond contractual tasks within an organization.

3. Taking things for granted.

Keep this in mind: More than 100 billion people have lived and died on this planet--the vast majority without electricity, running water, or antibiotics. In the very least take a minute every day to acknowledge you benefit from these things, as well as your many other blessings. Research has shown that gratitude can result in improved mood, better sleep, less fatigue and lower levels of inflammation.

4. Comparing yourself to others.

People do this all the time on Facebook. Yet a University of Houston researcher found a link between time spent on the social media site and depressive symptoms. Think about it--your Facebook friends mostly post only the good stuff that happens to them, while leaving out the bad. Do yourself a favor and remember that no one's life is perfect, regardless of what gets shared online.

5. Underestimating your willpower.

Maybe you've succeeded at stopping something--smoking, eating crap, or downing a bottle of wine in front of the TV every night--only to find yourself eventually caving because of feeling as if your willpower was depleted. It might be that your beliefs about willpower actually affected how much of it you have. Researchers have found that willpower appears to be a reflection of one's ideology. In other words, if you believe you have only a finite amount of self-control, you likely won't persevere in trying to reach difficult goals.