It means: Nobody is more blind than the person who decides he does not want to see. Often used in reference to prejudice and intolerance. Also: "There's none so blind as those who will not see."

Depending on the sentence in which you use the phrase, but the general Chinese meaning would be similar to "一意孤行，自以为是，刚愎自用，独断专行" etc. "none so deaf as those who will not hear" has the similar meaning.