Ask yourself this simple question: how confident would you need to be on a moral or political conclusion in order to work passionately for it? 99%? 90%? 75%? If you have such an action-threshold, and this threshold is high, well then yes, to let your passion flower, you may need to lie to yourself about your confidence. So that you might actually do something.
Would your overconfidence then lead you to do too many things too enthusiastically? If so, perhaps you’d do better to also allow yourself some other more graded psychological reluctance to passion, to counter this bias.But it would of course be even better if you could see the nobility and glory in doing your best as a limited but well-meaning creature. You shouldn’t need to be absolutely sure of a conclusion to work sincerely and passionately for it.
The emphasis is mine. In the first two paragraphs he articulates the trade off. Making an assumption, which is assigning something a higher prob of being true than you have evidence for, has the upside of allowing you to actually do things. But making an assumption also has the downside of distorting reality (e.g., making you overconfident), so we want ways to protect against too many assumptions.
In the last paragraph he says that we might circumvent the trade off by admitting that we might be wrong but pushing forward just as hard regardless. I doubt that's possible. Our brains are constantly computing probabilities and using those probabilities to determine policy implications, just as in Bayesian model averaging. So if we downshift the probability that an assumption is true, its relative policy implications also have to fall. There's a reason that overconfident CEOs are more innovative, and people crazy enough to be entrepreneurs are typically overconfident. All else equal, if you have less faith in your conclusions, you will work with at least slightly less passion towards them.