How do you deal with opportunity cost?

Hello everyone, i'm quite new here, but have been trading stocks for the last 2 years. In the past year I've made some mistakes, but one hurts me the most. I bought MU stock in December 2024 just after a pullback to about 84 USD - it then became roughly half of my portfolio, since I was this convinced that the memory prices will recover even if MU gives a bad guidance for 2025. And indeed, I did double my money and sold at the first real spike in September 2025 for about 160 USD. However, had I waited for just 4 more months, my gains would have been not 100% but 400% - a money which I could have allowed me to comfortably retire. I understand that you will say "a gain is a gain", but the idea that I did my research homework correctly, and then fucked up the execution really bothers me, particularly in the light that I now see my retirement disappear in front of my eyes. If I continue using the "secure" way via SnP500 and other ETFs it will take me 7-10 years to compensate the gains that I missed. How do you cope with such feelings? And do you think there are stocks right now which might still have some growth in front of them? Chips are expensive, Memory is ultra expensive, Space and Robotics is speculative and expensive... Would be very thankful for any advice.