Everything is easy and predictable in hindsight, if anyone believed that bitcoin is going to $4,000 from $100 at that time then they have excellent prediction skills, but even those didn't sell everything they owned and buy bitcoin, showing that the weren't certain. Everyone is free to make their own investment decisions on when to buy and when not to.
I am guessing that the point that the OP is trying to make is that a $100 is not that much money to spend on an investment. If that person would've spent that money for a single Bitcoin when the price was that low then they would have thousands of dollars.
If that same person did not purchase Bitcoin when the price was that low and they are trying to purchase Bitcoin at $4,600+ then they should've listened to the OP when they had the chance to purchase it when the price was at a $100.
Hindsight or not, it doesn't matter when the price of Bitcoin was really cheap to purchase and if they think Bitcoin was not worth the money then they shouldn't ever purchase Bitcoin.