The assertion being made is simple enough I'd say. The more one knows, the less they come face to face with things they do NOT know. As one's knowledge base increases, the result is, inevitably, a reduced drive to seek answers.
To put this in perspective, people often make decisions based on a "moral foundation" of some sort. For example, people inclined to believe in the common scientific explanation for the start of the universe, the Big Bang, are relatively unlikely to actually pursue research into an alternate explanation. In another example, people often gradually assume a political identity. The issues that are debated in a national forum are often far too complex to allow for an in depth examination of all the relevant factors and rather than pursue information people instead rely on their current base of knowledge to make a snap judgement.