The way billionaire John D. Rockefeller Sr. raised his children made his family remains rich for 7 generations.

Source: CNBC

According to statistics, most of the "famous" families in history have gone bankrupt in the 2nd generation, and maintaining to the 3rd generation is almost impossible. As a proof, there is an old saying "Every dog has his day". However, this is not true for all cases.
In the US, over 100 years, the Rockefeller family has been wealthy for 6 generations. Entering the 7th generation with 174 heirs, this family still maintains a huge fortune of more than $11 billion in 2019. It is known that the first person to bring glory and money to the family is John Davison Rockefeller Sr. (1839 – 1937) - business magnate and philanthropist, richest American of all time and richest person in modern history.
John Davison Rockefeller Sr. was the founder of the illustrious oil empire - Standard Oil Co. In 1916, the fortune of Rockefeller Sr. accounts for nearly 2% of the national economy, and if adjusted for inflation, his fortune would be worth about $418 billion today.
In addition to his business acumen, Mr. Rockefeller is also admired by posterity for his excellent parenting style. His advice to his descendants showed his outstanding vision and wisdom, thereby helping the next generation to prolong the glory and prosperity of the family.
During his life, the "Oil King" wrote his son a total of 38 letters. In a letter, he told his son one thing that surprised many people:

"Be stupid and smart"

"A person who is smart is a fool, and a person who knows how to play a fool is really smart." - Rockefeller wrote in his teaching letter. The "King of Oil" also recalled the story of his youth.

Source: India Rox

One day, while Rockefeller was walking on the street, a banker stopped him and asked him if he wanted to borrow $15,000. Incidentally, at the time, Rockefeller was also in need of some money. However, he did not show a rush, but calmly told the banker that he needed more time to think. Finally, Rockefeller signed a loan agreement with many favorable terms.
Apparently, Rockefeller's pretense of being stupid, having to think more about the loan, had let the banker's guard down. Because of that, he was able to negotiate with more favorable terms. Mentioning this event, the richest billionaire in modern history writes:
"Compared to showing cleverness, pretending to be stupid has a lot of benefits. Most importantly, it makes people lower their guard. Then you take the opportunity, quietly come out on top, and amaze everyone."
Talking more about why smart people should learn to hide their cleverness, Rockefeller explained to his son: Human nature is the most unpredictable. There are people who are just jealous of others’ talent and thus plotting to do harm to them. So, it's best not to show off your intelligence. The more boastful one person is, the easier it is to attract trouble. He will have more intense, negative competition.
The more you know how to pretend to be stupid, the more benefits you get. In fact, really smart people are quietly improving themselves to become stronger and braver, instead of bragging about themselves.
H/T: CNBC