This quote suggests that those who are wise are often filled with doubts, because they understand the complexity and uncertainty of the world. They are aware that there is much they do not know, and so they question, they ponder, and they hesitate. They understand that every action has consequences, and every truth has a context. Therefore, they are often filled with doubts and are constantly seeking knowledge and understanding.

On the other hand, the quote implies that those who are dull or less intelligent are often certain of their beliefs and actions. This is because they lack the awareness or understanding of the complexity and uncertainty of the world. They see the world in black and white, right and wrong, and so they are certain of their beliefs and actions.

This quote can be applied to today’s world in many ways. For instance, in the realm of politics, we often see that those who are certain of their beliefs are often the loudest and most influential, while those who are wise and understand the complexity of the issues are often filled with doubts and therefore less assertive. This can lead to a situation where the loudest voices, rather than the wisest, dominate the discourse.

In terms of personal development, this quote suggests that it is important to cultivate wisdom and understanding, even if it means living with doubt and uncertainty. It is better to question and seek understanding than to be certain and ignorant. This involves being open to new ideas, questioning our own beliefs, and seeking to understand the perspectives of others. It also means being comfortable with uncertainty and doubt, and understanding that these are not signs of weakness, but rather signs of wisdom.