$40 dollars back then was about $500 today or about the equivalent of a plane ticket across the USA. Would you sacrifice 1 plane ticket to make your family became very wealthy?? The other insight that this is meant to demonstrate is how important it is to pick great companies that will yield you very nice returns. There's an astronomical difference between 7 and 10% when you compare it over 95 years. A difference of $25,000 to $350,000 to be more exact...
Funny personal note on this subject. When Coke went public, my great grandfather was offered stock in the company. His response? "Why would I want to buy stock a sugar water company?". Ugh!