It's by the English born American poet and author, Edgar A. Guest.
Can't
by Edgar A. Guest
Can't is the worst word that's written or spoken;
Doing more harm here than slander and lies;
On it is many a strong spirit broken,
And with it many a good purpose dies.
It springs from the lips of the thoughtless each morning
And robs us of courage we need through the day:
It rings in our ears like a timely sent warning
And laughs when we falter and fall by the way.
Can't is the father of feeble endeavor,
The parent of terror and halfhearted work;
It weakens the efforts of artisans clever,
And makes of the toiler an indolent shirk.
It poisons the soul of the man with a vision,
It stifles in infancy many a plan;
It greets honest toiling with open derision
And mocks at the hopes and the dreams of a man.
Can't is a word none should speak without blushing;
To utter it should be a symbol of shame;
Ambition and courage it daily is crushing;
It blights a man's purpose and shortens his aim.
Despise it with all of your hatred of error;
Refuse it the lodgment it seeks in your brain;
Arm against it as a creature of terror,
And all that you dream of you someday shall gain.
Can't is the word that is for 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."