Can't is the word that is foe to ambition,
An enemy ambushed to shatter your will;
Its prey is forever the man with a mission
And bows but to courage and patience and skill.
Hate it, with hatred that's deep and undying,
For once it is welcomed 'twill break any man;
Whatever the goal you are seeking, keep trying
And answer this demon by saying: "I can."

Can't, stanza 4, p. 54. - A Heap o' Livin' (1916)