The central values by which most men have lived, in a great many lands at a great many times--these values, almost if not entirely universal, are not always harmonious with each other. Some are, some are not. Men have always craved for liberty, security, equality, happiness, justice, knowledge, and so on. But complete liberty is not compatible with complete equality--if men were wholly free, the wolves would be free to eat the sheep. Perfect equality means that human liberties must be restrained so that the ablest and the most gifted are not permitted to advance beyond those who would inevitably lose if there were competition. Security, and indeed freedoms, cannot be preserved if freedom to subvert them is permitted. Indeed, not everyone seeks security or peace, otherwise some would not have sought glory in battle or in dangerous sports.

Justice has always been a human ideal, but it is not fully compatible with mercy. Creative imagination and spontaneity, splendid in themselves, cannot be fully reconciled with the need for planning, organization, careful and responsible calculation. Knowledge, the pursuit of truth--the noblest of aims--cannot be fully reconciled with the happiness or the freedom that men desire, for even if I know that I have some incurable disease this will not make me happier or freer. I must always choose: between peace and excitement, or knowledge and blissful ignorance.

Source: A Message to the 21st Century | by Isaiah Berlin | The New York Review of Books