Best decision - I was absent from class one day. I have talked about this on Quora. I'm just copy-pasting the same answer - One day, I was absent from school in class 10 (that's sophomore year for folks in the USA). And my absence started a chain of events that has changed my life in the most amazing way possible. For a little backstory. Due to some unavoidable and horrible incidents, I used to be pretty bad at Maths. I didn’t like Maths at all. In fact, I used to love Chemistry. My Maths grades were horrible. Once or twice I scored well, but that was completely due to easy questions, not due to my skills. My house is near Indian Statistical Institute, and they organize a Maths competition for class X (now it’s for class IX and XI, I think) named Mathematical Talent Reward Programme (MTRP). Now coming to the real story. One day, I was absent from school. Turns out that day, they distributed the application forms of MTRP. I was least bothered about it - “Ew! Maths exam!!” But my friend, philosopher, guide, teacher, and best friend Ayan Biswas insisted I take the exam. “Come on! It’s just one exam!” I asked our Maths teacher for one form. “Erm. All the forms have been distributed.” That could have been the end. But I, being the idiot that I am, mentioned this to my mom, and mom, being an Indian mom, took me to a coaching center in my locality which is famous for its collaboration with ISI. The owner of the center knew me from my childhood. Not only was our house near the coaching center, but the house adjacent to this center was also my maternal uncle’s house. In my childhood, my cousin and I used to scream through the window of the coaching class. So he at once gives me a form, along with the names of a few books. I bought the first one - An Excursion in Mathematics. The first chapter was “Number Theory,” and boy! I was mind blown. Before that, I never realized that Maths is not only about weird calculations but also logic and observation. It changed my conception of Mathematics, and I got fully devoted to Maths. I used to carry my precious Maths books all day and used to read them during any kind of break I got. In fact, I stopped everything else and drowned head-first in Maths. The result? I passed class 10 with 100% and 12 with 98% and did M. Sc. in Maths. As for the worst decision: I didn't see my grandmother when she died because I was scared. I was only 9, but I was afraid to face her. I won't be talking too much about it since it brings back some traumatic memories.