He's been reading Ben Franklin about the vital importance of doubt:
For having lived long, I have experienced many instances of being obliged by better information, or fuller consideration, to change opinions even on important subjects, which I once thought right, but found to be otherwise. It is therefore that the older I grow, the more apt I am to doubt my own judgment, and to pay more respect to the judgment of others.
Next up: try some Hume, Hugh. Or even Burke. At some point in the future, you might even become a conservative.