“Quasi tutti gli uomini possono resistere alle avversità, ma se vuoi testare il carattere di un uomo, dagli potere.”

Originale

Nearly all men can stand adversity, but if you want to test a man's character, give him power.

Widely attributed to Lincoln, this appears to be derived from Thomas Carlyle's general comment below, but there are similar quotes about Lincoln in his biographies.
Adversity is sometimes hard upon a man; but for one man who can stand prosperity, there are a hundred that will stand adversity.
Thomas Carlyle (1841) On Heroes and Hero Worship.
Any man can stand adversity — only a great man can stand prosperity.
Horatio Alger (1883), Abraham Lincoln: The Backwoods Boy; or, How a Young Rail-Splitter became President
Most people can bear adversity; but if you wish to know what a man really is give him power. This is the supreme test. It is the glory of Lincoln that, having almost absolute power, he never used it except on the side of mercy.
Robert G. Ingersoll (1883), Unity: Freedom, Fellowship and Character in Religion, Volume 11, Number 3, The Exchange Table, True Greatness Exemplified in Abraham Lincoln, by Robert G. Ingersoll (excerpt), Quote Page 55, Column 1 and 2, Chicago, Illinois. ( Google Books Full View https://books.google.com/books?id=JUIrAAAAYAAJ&q=%22man+really%22#v=snippet&)
If you want to discover just what there is in a man — give him power.
Francis Trevelyan Miller (1910), Portrait Life of Lincoln: Life of Abraham Lincoln, the Greatest American
Any man can handle adversity. If you truly want to test a man's character, give him power.
Attributed in the electronic game Infamous
Misattributed