the nature of people to blame others for their own mistakes or shortcomings
Explanation:
You can see how the author makes fun of it and points out this behavior in this part of the excerpt:
<em>"[...] I knew men well enough to know that when they find they've given a tramp a million-pound bill when they thought it was a one-pounder, they are in a frantic rage against him instead of quarreling with their own near-sightedness[...]"</em>
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They would not blame themselves for giving away that money. They'd not even think about how they were the ones to commit such mistake. They'd blame the one that had the note because otherwise, it'd be their fault.
