Recently my son asked me why he needs to do mental math when calculators exist. I told him if he doesn't, he will make irrational decisions throughout his life. Let me explain. Say you see two packs of snacks. A 500g pack for ₹100, and a 200g pack for ₹45. Which one should you buy? The math is not at all hard, but people who are scared of mental math will not do it. This is not such an important decision that you pull out a calculator for it. So you make the decision on vibes - say ₹100 "looks too high", or that the smaller pack costs "less than half of the biggest one" or some such. The problem isn't that you made a poor decision on snacks. It is that if you do this repeatedly, you train your mind to make decisions on vibes. Over time your reasoning muscle atrophies - so you start relying even more on vibes. Before you know it, you are taking even big decisions on vibes. Should I rent or buy a house? Let's decide based on "EMI affordability", not rental yield. Should I invest in this IPO? I have heard of the company's brand so I'm all in. It isn't only financial or quantitative decisions either - in my mind the math muscle and the logic muscle are closely correlated, so a decline in one certainly affects the other. Like the Arab who let the camel's nose inside the tent, fear of math is the first step towards thoughtlessness, and needs to be nipped in the bud. Intellectual laziness starts with snack prices.