The method of tenacity described by Peirce and the propensity to selfdeception reported (and diligently resisted) by Darwin are both ways to keep our relevant beliefs safe from the brunt of unfavourable or just unfavourable–looking matter. Their common denominator is the notion of avoidance. In the one case this is achieved by the methodical looking away from what might damage the soothing illusion at issue, and in the other by our spontaneous tendency to skip from, undervalue and erase from the field of awareness facts and thoughts which prove uncomfortable to dwell upon. Both mechanisms bring out the involvement of the thinking subject's desires and emotions in the process of belief–formation – they show how this interference may affect the workings of the understanding and hence impair cognition.

These mechanisms for the protection of belief can be seen as instances of what has been recently described, in more general terms, as the phenomenon of ‘theoretical akrasia’: ‘We notice or allege a case of theoretical akrasia whenever we speak of refusing to see, of not wanting to know, and in at least some of the cases where we accuse someone of self–deception, or of living in a fool's paradise’. The term akrasia here, it may be noted, is borrowed from Aristotle's ethics, where it is used to refer to the failure, by an individual agent, to act in line with his own opinion about what he should do when the time to act comes.