We had a lot of time to invest in Bitcoin when the price was still quite low, in 2015 or even 2017, the opportunity was already there for everyone who focus on it. However, many of us were scared of Bitcoin at that time. Some others assumed it was a scam or something that won't last. Others didn't understand it or were too scared to take the risk. The fact is that we all had the same chance at that time, what we did with that opportunity is what matters today. Some people who started buying Bitcoin at that time made some mistakes, such as selling too early, not buying enough, or trying to trade instead of holding. However, as you said, mistakes are a normal part of learning. What matters most today is that we don't keep making the same mistakes. We must learn from our experiences and make better decisions for the future.
You also need to understand that within those years you mentioned not many people knew about bitcoin because if you do a research on people who knew about bitcoin in 2015 and 2017 you will see that very low number of people knew about bitcoin but in 2021 after the price of bitcoin hit an ATH of $69k, more people began to know about bitcoin and also when the price of bitcoin hit an ATH of $73k in March 14, 2024, the news also brought in new investors and after the US election when the price hit $100k, it created so much excitement that led more people to invest in bitcoin. What i have to say is that those who could have invested earlier when the price was very much affordable but couldn't was because of several reasons such as not believing in the growth of bitcoin and as then bitcoin was also facing severe criticisms where people were scared away because they thought it was a scam. I don't even care who do not invest when the price was much cheaper, but if they invested after finding out that those narratives were false that should be the best decision and no need to deliberate on their past mistakes for not buying since bitcoin didn't gain much recognition then.