The problem is that the believer (Farmer Franco) was right for the wrong reason, but this turned out irrelevant. It's likely that in many such cases, his reasoning was only a confabulation for a deeper intuition about how Daisy behaves, and so, it was not pure luck. Epistemologically the problem is that often beliefs are not based on 'if and only if'--aka necessary and sufficient--conditions, so your beliefs are often right for wrong reasons, and so you don't really understand not only those beliefs you have that are wrong, but those that are right as well. As Keynes said, right policies are invariably chosen for the wrong reasons, so one can't too worked up about the fact that 'someone on the internet is wrong.' Given any big debate has two sides (eg, raise or lower taxes to increase welfare), you have only a 50% chance of being correct. As there are only a few out of many plausible reasons for having the right belief, odds are you are wrong about your reasoning more than your are wrong about what to do.
Reason is to man a great gift over and above the raw instinct and emotions we share with the great apes. It should help us find better solutions faster, which is best demonstrated by our technology and increased life spans. But we shouldn't trust reason and rhetoric too much, as traditions and instincts have wisdom too.
Comments