There’s none so blind as those who will not see.
When the blind lead the blind, both shall fall into the ditch.
Similar concept: The blind leading the blind.
In the country of the blind, the one-eyed man is king.
There’s none so deaf as those that will not hear.
A fool and his money are soon parted.
Ignorance is bliss.
Similar proverb: Where ignorance is bliss, ‘tis folly to be wise.
Penny wise, pound foolish.
Related proverb: An ounce of prevention is worth a pound of cure.