Question

What makes Montaigne so skeptic

Answer 1

Montaigne’s skepticism is a result of his studies of the ancient skeptical traditions.
His skepticism is more based on the question, “What do I know?”
Montaigne’s remarks are usually preceded with the possibility of them being a mistake such as “I think…”, “To some extent…”, etc. 

Answer 2

Michel de Montaigne was a philosopher of the French Renaissance, known for making the genre of essays particularly popular.

One of the defining features of Montaigne's thinking is his skepticism. Montaigne's skeptic writing was based upon the skepticism common in ancient literature and philosophy, particularly that of the Greeks. He is particularly close to the ideas of the Pyrrhonists. One of the features of this type of thinking in his work is the encouragement of doubt, and the acceptance of the limits of knowledge.