This may be just another way of saying that none of us is perfect and that we mustn't therefore allow surprise at the discovery of the axiom to ruin what otherwise exists. Certainly the realization may prompt at least temporary withdrawal or cooling. But in the end it has always been my opinion that I am far more entertained by people to know their true nature than to imagine hidden value rather than unpredictable dangers. The human animal is as visceral as any other and it requires little philosophic posture to open the gateways to the combined import of instinct and necessity - perhaps features of existence which are far more compelling than altruism or morality will ever be. In fact I tend to view the seeming disloyalty of deceitful conduct as more a product of need than preference, which is to admit (or perhaps submit to) its manifest native cause. How frequently we misinterpret the actions of others when we disguise the reason with unfaithfulness. True, there are occasions of intended subversiveness. But that in itself adds nothing to the authenticity of the failing as a personal assault upon oneself.
There is another self-reflective aspect to this so-called insight into the machinations of others. And that is the related adage that criticism is the best autobiography. Time and again I have learned that the appearance of discernment which I and others have regarding the interpretation of the apostate currents of our fellow malingerers is nothing more profound than the sensibility to private motive. Put another way, "We see in others what we see in ourselves". This frank admission tends to diminish both the value and repugnance of the duplicitousness. The understanding may be grounds for changing the character of the relationship; but once again it must be considered very carefully before abandoning the relationship. A far wiser choice is to use the knowledge to increase the depth of the alliance. Keeping in mind that few if any of us is ever likely to change greatly, it is readily acceptable to continue to association with a watchful eye.
Though it hurts at times to concede that the alleged favour from another person is nothing more than a repeated habit practiced with many other than oneself, we mustn't allow this lack of singularity to misdirect the substance of the friendship. If indeed there were any useful conclusion to be drawn from the perception it is that the very commonality of the behaviour is the secret to its performance. Even the most clever people seldom correspond with invention beyond mere frequency - though it does take time for outsiders to establish the constant course of action.