Noticing differences greatly assists survival… up to the point of diminishing returns, especially for a thinking animal like us. Even so, the naïve acceptance of difference as a true portrayal of reality would seldom have been a problem for our hunter-gatherer ancestors, given their down to earth circumstances.
Conversely, our naive acceptance of difference as a true depiction of reality causes anxiety, given the less down to earth nature of civilization. Civilization, by taming the wilderness, removes the natural stresses that would otherwise counterbalance anxiety. Before we know it, we become neurotic nitpickers in one way or another.
Chapter 56 hints at how to mitigate the ‘difference bias’ that so easily swamps cognition and ramps up stress: Block the openings; Shut the doors. Blunt the sharpness; Untangle the knots; Soften the glare; Let your wheels move only along old ruts. This is known as mysterious sameness.
It helps to know where we are on the bell curve of balanced awareness, i.e. between devoting too much or too little credence to differences. As with maintaining physical balance, noticing when we near the tipping point is crucial. Chapter 64 says, Deal with a thing while it is still nothing. That means watching the mind as warily as possible. As chapter 71 ends, It is by being alive to difficulty that one can avoid it. The sage meets with no difficulty. It is because he is alive to it that he meets with no difficulty. The difficulty here is our innate tendency to focus excessively on differences, seldom on similarities. I assume that is because noticing difference is of much greater evolutionary / survival value for creatures living in the wild.
Much of the difficulty lies in what we think we need. Desire (need + thought) pulls perception to gloss over differences at times, and yet makes mountains out of molehills of difference at other times. Our own mind and its thoughts trap us. No wonder chapter 71 warns us that thinking that one knows will lead to difficulty.