Is doimhin é poll an amhrais.

Deep is the hole of doubt.

Note: "Doubts are more cruel that the worst of truths." Jean Baptiste Poquelin Moliére, Le Misanthrope, Act III, Scene vii. Doubts can cripple you. They can freeze you into inaction. Falling into doubt can be like falling into a deep hole; it is hard to get out.

Attempt the end, and never stand to doubt;
Nothing's so hard but search won't find out.
Robert Herrick, Heperides

Or in the words of copy writer for a more modern sneaker manufacturer, "Just do it."

Note also: Proverbs are like fossils. They tend to preserve old forms. This week's proverb is no exception with the spelling of the word "doimhin." This was the most common spelling for the Irish word for 'deep,' before the official standard spelling was introduced in the 1940's. The official spelling is 'domhain.' However, the official spelling for the genitive form is the more retrograde 'doimhne.'