The attempt and not the deed

Confounds us.

William Shakespeare (1564-1616): Macbeth. Act ii. Sc. 2.

Our doubts are traitors,

And make us lose the good we oft might win

By fearing to attempt.

William Shakespeare (1564-1616): Measure for Measure. Act i. Sc. 4.

Attempt the end, and never stand to doubt;

Nothing's so hard but search will find it out.

Robert Herrick (1591-1674): Seek and Find.