Gortsby learned what he thought he already knew. Don't be too trusting. Gortsby in his own cynicism was already on to people like the young man. Still, the young man tricked Gortsby into giving him his money.
The real lesson here is that people are often too trusting by nature. Gullible is a word that comes to mind. Naive is another word that fits this story. Truly, the cynical man Gortsby already stated that the defeated come out at dusk. He was already aware to be on guard. In fact, he concluded that the young man was a con artist because he could not produce a bar of soap.
Ironically, the bar of soap produced itself and turned the cynical man's cynicism into trust. Oh, how a small bar of soap can change one's thinking into a cleansing thought.
Again, Gortsby learns a lesson. No doubt, Gortsby has every right to be cynical. All too often, we as trusting human beings get burned. The lesson is that the human heart desires to trust unconditionally. It is in human nature to give one's heart away. Even though Gortsby prides himself on understanding the defeated ways of mankind, he too fell for the con artist. He was all too ready to pour out his sympathy with nothing to gain in return. Some consider it an admirable quality. Saki would consider it foolish.
The reader learns a lesson right along with Gortsby. Don't be too trusting. To borrow a cliche: if it sounds too good to be true, it probably isn't. Don't talk to strangers, especially right before it gets dark.
Saki, in all his infinite wisdom, through men like Gortsby and the young man, teaches a lesson on the danger of believing everything people say:
Saki came to the short story as a satirist and never averted his eye from the darker side of human nature, a place where not only social ineptness, pomposity, and foolishness are rooted but criminality as well.