A prince ought to have no ...

A prince ought to have no other aim or thought, nor select anything else for his study, than war and its rules and discipline; for this is the sole art that belongs to him who rules, and it is of such force that it not only upholds those who are born princes, but it often enables men to rise from a private station to that rank. And, on the contrary, it is seen that when princes have thought more of ease than of arms they have lost their states. And the first cause of your losing it is to neglect this art; and what enables you to acquire a state is to be master of the art.
A prince ought to have no other aim or thought, nor select anything else for his study, than war and its rules and discipline; for this is the sole art that belongs to him who rules, and it is of such force that it not only upholds those who are born princes, but it often enables men to rise from a private station to that rank. And, on the contrary, it is seen that when princes have thought more of ease than of arms they have lost their states. And the first cause of your losing it is to neglect this art; and what enables you to acquire a state is to be master of the art.

Quotes from the same author

No enterprise is more likely to succeed than one concealed from the enemy until it is ripe for execution.
Men in general judge more from appearances than from reality. All men have eyes, but few have the gift of penetration.
Men are less hesitant about harming someone who makes himself loved than one who makes himself feared because love is held together by a chain of obligation which, since men are wretched creatures, is broken on every occasion in which their own interests are concerned; but fear is sustained by dread of punishment which will never abandon you.
Many have imagined republics and principalities which have never been seen or known to exist in reality; for how we live is so far removed from how we ought to live, that he who abandons what is done for what ought to be done, will rather bring about his own ruin than his preservation.
A wise prince then...should never be idle in times of peace but should industriously lay up stores of which to avail himself in times of adversity so that when fortune abandons him he may be prepared to resist her blows.