Let me tell you a story.
A and E were both very smart people. A had an IQ of 153, and 2 PhDs, one in sociology and one in psychology. E was a writer and artist with an IQ of 146, and she wrote many papers and articles on business strategy.
In September 2000, A and E had a daughter.
Their daughter, named J, was very smart. Like her mother, she loved writing and won many awards. By the time she was 15, she already had 2 of her books published. She started reading at a phenomenally early age (2 years old - most children start reading at 6 or 7). She had an IQ of 149 and was a creative genius and constantly created artistic and literary masterpieces.
In March 2003, A and E had a son.
Their son was also named J, but let’s call him Jay for convenience’s sake. Jay was a mathematical genius and smarter than even his sister and his parents, having an IQ of 165. At the age of 8, he beat the national chess champion in 4 minutes and 36 seconds. Thanks to his photographic memory, he easily scored a 100 (and sometimes more due to extra credit) on every test and exam without even trying. He never bought a calculator to school because he could work out the sums even faster than the calculator could.
Buoyed by the delight of their two genius children, A and E decided to have another child. In June 2005, they had a daughter named L. Since their first child had been a literary genius and their second a mathematical genius, maybe their third would be a scientific genius and go on to win a Nobel Prize.
But L was not smart. A and E had L go for an IQ test, where she scored a measly 107. She progressed at a boringly average pace, learning to read at the average age (7) learning to write at the average age (8) and learning to do math at the average age (6).
No matter how hard she tried in class, she could never get a 100 on her tests like Jay. No matter how hard she tried to learn, she could never make beautiful drawings like J.
L did her best to compensate for her lack of smartness, studying hard and taking on as many after-school activites as she could. A and E encouraged her, telling her that it didn’t matter if she was bad at math and couldn’t understand the inner workings of language, but she read the truth in their faces: It would still be better if you were smart.
J and Jay loved their little sister, but L could see the pity in their eyes whenever she struggled to complete homework or write an essay. Once, when L could not finish a project because of all her after-school activites and resigned herself to missing the deadline, J snuck into her room while she was asleep and finished writing the paper for her in ten minutes. When L found out, she didn’t speak to J for a week.
L suffered all her life from the prying questions of teachers and friends wondering why she wasn’t as smart as the rest of her family. She never spoke up during the philosphical and scientific debates her family had at the dinner table because she couldn’t understand what they were talking about. L felt a deep shame whenever she saw one of her siblings breeze through something she had stressed over. She could feel the quiet disappointment of her parents whenever she failed an exam one of her siblings had taken ten minutes to study for.
L became very stressed and worn thin. She had no friends because she spent all her time studying or at after-school activities. She didn’t have any hobbies because she never even considered having something called free time.
I was L. I’m still L, and my life has always been like this because I was unlucky enough to have the smart gene skip a generation in me. So to answer your question, yes, sometimes smart people have stupid kids, and that’s just the way it is.