In most cases, a truth—especially a startling or upsetting truth—should be given in small doses. This is common wisdom: even when the police, for example, show up at a person's door to report a death, although the truth has to be delivered quickly in that case, their appearance at the...
door, their sober demeanor, and usually their prefacing statement about bad news to report will prepare the person for the startling truth they are about to receive.
Literature, one of the best vehicles for discovering truth, supports the idea of the wisdom of revealing the truth in small doses. We see the terrible effects, for instance, when Oedipus suddenly realizes the truth that he has married his mother and killed his father—he blinds himself in anguish, while his wife/mother commits suicide. A more gradual approach might have averted these tragedies.
Poet Emily Dickinson expresses the idea of gradual approach to truth when she says, "Tell the truth but tell it slant." Too much truth all at once is too blinding. The idea of a sudden truth as blinding (disabling) hits its fullest expression in the Apostle Paul, who was so stunned by the appearance of the Holy Spirit telling him to support the Christians that he temporarily went blind—this (to him) truth so upended his world that he was temporarily disabled.
Stephen Benet expresses this idea directly in his short story "The Waters of Babylon." The village priest's son John comes home with the information that what his people think of as gods are simply humans who destroyed themselves. His father tells him not to simply blast out this truth, because it will be overwhelming and destructive to the people if not revealed gradually.
Even Galileo's best friends, highly educated people, were stunned and disbelieving when he insisted the earth travelled around the sun and not vice versa, as the evidence of the senses seems to show the sun revolving around the earth. It took a long time for Galileo's truth to stick. This seems to be the way it goes, so gradual revelation is best to get people used to new ideas.