"That's metaphysics, my dear fellow. It's forbidden me by my doctor, my stomach won't take it"

This quote by Boris Pasternak is a humorous way of expressing the concept that some things are too complicated to comprehend. Metaphysics is a branch of philosophy that handles the nature of reality and the relationship between mind and matter. By saying that it is forbidden by his medical professional, Pasternak is suggesting that it is too hard to comprehend which it would be detrimental to his health. He indicates that his stomach won't take it, meaning that it would be too much for him to manage. This quote is a humorous method of expressing the concept that some things are too complicated to comprehend and that it is best to leave them alone. It is a suggestion that it is necessary to understand our limits and to not press ourselves too far.