"All belief is based on suspect reasoning"
This aphorism is definitely one that shouldn't be taken so literally because yes, we all possess some well reasoned beliefs. But if our goal is to see beyond our biased view of reality, and our autocentric mind is certainly biased in favor of its self-reasoned beliefs, the reasoning that all belief is based on suspect reasoning may suggest to our mind that it not be so sure about its convictions. It's a reminder to leave a little wiggle room in any belief in case reality turns out to be not so simple as the reasoning that led to the belief.
This maxim could also be shortened to "Suspect one's beliefs" – a wise policy overall, but especially if one's beliefs are based on someone else's reasoning – in which case belief is actually based on the absence of reasoning.