How much does prejudice/partisanship/brainwashing block the path to true understanding? 100% ?

If a person allows prejudice/partisanship/brainwashing to block their path to true understanding then that person has a major problem. We are all individuals with the ability to think individually. To make our own choices, and to hopefully take responsibility for our own action when things go wrong because of our own stupidity. Blaming other people or blaming circumstances for keeping you from true understanding is a cop out, cowardly, and dishonest.

It can be any measure of any percent depending on the one who is guilty of said antics.

So many people have been influenced by the deceptions of the world. satan has them wrapped around his little finger, and they don't have a clue. Many of these consider themselves Christian, yet totally reject the bible's counsel over the so-called worldly wisdom. (John 8:44)