Tomas Aquinas explains that blindness is a state of deprivation, the mole and the blind man are deprived of view, one by his own gender, the other by accident. A deprivation is something that by nature should be possessed but for some reason we do not have. By nature is understood what the being tends towards his development. The Bible speaks about the deprive man, of the blind man.
The quote: "when a blind man guides a blind man, both fall into a pit" in the Gospel of Matthew 15:14 must be understood in the context of the biblical teachings. The gospel teaches us: "No one can see the kingdom of God unless they are born again", John 3:3; also: "But whoever lives by the truth comes into the light" John 3:21.
"To see" in the gospel means "to perceive with the mind", in other words to capture with the gift of knowledge, to"enlighten" us through the gift of wisdom, which is the taste for the truth.
The gift of knowledge is the "eye of the mind", this gift is one of the seven gifts of the holy spirit, the gift of knowledge is the same intelligence of God. Human reason is not enough, reason is affected by passions. The gift of knowledge is in practical terms "progressive thinking", it is the thought in which prevails the higher faculties of the mind: intuition, inspiration and creativity. It is through this gift that we perceive, capture the plane of the truth.
To perceive the Kingdom of God is to capture through the gifts of wisdom and knowledge (the spiritual gift of knowledge is also called understanding), remember "Here is wisdom, let the person who has understanding calculate the number of the beast", Revelation 13:18 .
This teaching reminds us of the importance of reason ethically, not to act like fools. The meaning of the phrase tells us that when a fool follows another fool, the two fall in disgrace. When we reason ethically, that is, when we properly evaluate when something is wrong or not, we learn from our mistakes and those of others, we work to improve, to minimize the error and the suffering and consequently we attain the true happiness and not the opinionated happiness.
Self-help books are a clear example that when explanations are superficial, or to say when we seek success focusing in an emotional positivism (optimism) ignoring our neighbour, the failure is clear. "View" is the opposite of being "blind", that means to understand that we live in an "Ethical Universe", that is, a universe governed by ethical laws (law of the return, golden rule) and therefore we must understand them and act according them.