He has discovered knowledge that we do not know and isn’t telling us; he is keeping it a secret.
He is “reserved” about a subject which is telling that he is keeping a secret and is only telling what we need to know and nothing more.
He doesn’t want to lead us on by getting us to excited about his discovery. telling us that if we no to much that we become our own “destruction and infallible misery”.
He wants us to learn from his mistakes and to use his advice for he should know as he found out first hand how truly dangerous it really is know so much knowledge.
him saying all these things if foreshadowing that something dramatic is about to happen form all the knowledge he has got and how it had a major effect not only on him but on the world of science.
Victor Frankenstein is telling the captain his story of how he came to know all this knowledge because he can see in his eyes the wonder and the curiosity of the secret that Frankenstein has. Victor is slowly telling him the story but once the captain knows the knowledge that Frankenstein does he will wish that he dint know. As Frankenstein said ‘how much happier that man is who believes his native town to be the world, than he who aspires to become greater than his nature will allow’, another way of saying this is like if someone stays at home and sticks to their routine and in their own comfort zone will be more happier than a person that pushes out of their comfort zone and fails. Frankenstein says that knowing and having so much knowledge is dangerous compared to knowing some knowledge.