Jabez Wilson thinks he is learning something valuable while he is copying the articles in the Encyclopedia Britannica, but he is really only acquiring a temporary knowledge of certain facts, most of which will eventually be forgotten. A real education does not consist of the accumulation of a lot of knowledge, much of which is better off kept inside a book like the Encyclopedia Britannica. A real education includes thinking and discussing as well as simply reading. A person who aspires to be educated should think about what he or she is reading and deal with it interactively--that is, to relate it to his or her own experience and common sense. As Bacon says in his essay "Of Studies, one should "weigh and consider" what is being read.
Crafty men contemn studies, simple men admire them, and wise men use them; for they teach not their own use; but that is a wisdom without them, and above them, won by observation. Read not to contradict and confute; nor to believe and take for granted; nor to find talk and discourse; but to weigh and consider. Some books are to be tasted, others to be swallowed, and some few to be chewed and digested; that is, some books are to be read only in parts; others to be read, but not curiously; and some few to be read wholly, and with diligence and attention.
Wilson will always be simple and naive because he is lacking in intelligence. He could copy all the articles in all the volumes of the big encyclopedia and still be simple-minded and uneducated. Possibly the most valuable lesson he learned from his eight weeks of copying from the first volume of the encyclopedia occurred when he found the notice that the Red-Headed League had been dissolved. That was when he started using his own brain for something besides a repository for factual information, most of which was of no practical use to him.
The key idea that Conan Doyle seems to be projecting which could be a life lesson is that if something seems too good to be true, it probably is. Jabez Wilson is taken in twice due to his greed and lack of common sense.
Vincent Spaulding offers to work for half of the pay that other assistants request. Wilson is aware of this, and takes advantage; not realizing that he is the one being taken advantage of. As Holmes says-
From the time that I heard of the assistant having come for half wages, it was obvious to me that he had some strong motive for securing the situation.
Similarly, Wilson cannot see the farcical nature of an organization such as the Red Headed League offering large amounts of money for red haired men to copy out the Encyclopedia Brittanica. He sees only that he can make extra money with very little work and a qualification he was born with.
Wilson’s gullible and avaricious nature are used against him: he aims to get a lot for a little as, ironically, do the criminals who dupe him.