why the fuck are parents so stubborn

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everything i try to explain to them they say it's wrong because they think i saw that from ai whatever it is whether it's skincare, nutrition or gym and everything i say immediately gets deleted from their mind because "it's from chatgpt" and i try to give them information that i read from studies but no they just won't listen. For example they say that if i don't eat at least one meal my mom makes that i won't grow and the way she makes everything is just loading fucking olive oil on everything and one meal has probably a 1000 kcal and 0g p and they say it won't make a difference in me gaining muscle or weight and i try to explain to them that it doesn't matter whether i get my calories from their food or the food that i make as long as it's at least at maintance calories and that i will grow the same in height but no theirs is healthier somehow. My mom said that lamb is the leanest meat and that it's leaner than chicken, and when i was eating their food i was fat af and they said that i look fine and that I'm healthy but i was overweight like 25 bmi. And they just think they are so much smarter than me in every aspect just because they are older. My dad said that when he was young he ate whatever he wanted and he was an athlete and didn't gain weight and now he has 120kg fat af and i tried to help him lose weight but he is literally joking with me like i try to at least swap regular coke with coke zero and he says it's bad and it has chemicals even though he is taking years of his life by being fat but no I'm always wrong.