Fear of Success:

This sounds strange, but it does exist. The fear of success has been linked with the existence of low self-esteem.
This is a scenario whereby a person feels undeserving of a certain level or extent of success!
Education and skills play roles in achieving success, but enduring success comes with the belief that a person is deserving of it.

Like other kinds of fears, this also could have been established during early childhood or during teenagehood.

The desire for success may be apparent, but the subconscious is not in sync with the conscious desire. And psychologists say that a lot more is going on in our subconscious than there is happening on our conscious minds.

When these persons manage to attain improved successes, somehow self-sabotaging behaviours kick in, and they fall back to levels they subconsciously can accommodate and relate with.

Sometimes, fear of success comes from prolonged association with a certain status quo. When a person learns and accepts a certain level of success as their peak, they can start to unconsciously reject successes that push beyond those peaks. The rejection is unconscious because, such a person does not know that surmounting their regular peak activates them on a self-sabotage behavior. When they fall back below their regular peak, their sense returns, self-sabotage ends, and the struggle continues! They are thus held in a cycle, by beliefs that may no longer serve them good purpose if they do want to hit higher ground.