You know the story about the elephant whose one leg used to be tied using a small rope since the time he was young and he used to experience a lack of freedom in moving around wherever he wished. At that age, the small rope was enough to tie the elephant. As the elephant grew bigger, he possessed the physical strength to break the rope and wander around freely but instead of making use of his strength to break the rope, he did not do so. He remained confined to the same small region where he used to be tied because his mind was conditioned that he cannot break the rope, which is an example of a mental limitation.
In a similar manner, the inner region of our mind is the place where we as children got used to being tied with the different types of ropes of a lack of optimism or positivity. E.g. I cannot do well or I am not good enough or I am not as successful as others or I am low on self-confidence or I am an under-achiever. These ropes in many people are so strong that a time comes when situations of success have arrived in their life in different forms as they have grown up and they have achieved reasonably in different spheres of life. At that time they can easily break these different ropes, but they still remain low on optimism.