describing bitcoin this way makes it appears like ponzi scheme, as the investment of new commers are what is being used to pay the already existing customers on the platform, at the end of the day if they don't get new sign-up and people ready to fall victim of their scheme, you realize that the platform willl short down, where there are always people who pay for the rich of others, others get rich using the downfall of the next person, At the end of the day their is always a a winner and a losser.
But when it comes to bitcoin, We will always have those who are willing to buy and those who are willing to sell, and the value is determined by what the masses are willing to pay for it and based on its demand in the market.
Selling at any particular time is a choice; the same is also applicable to buying. If you decide to sell when the price is dumping and you happen to record some losses, that's on you, and the mistake that you made yourself shouldn't be shifted to others.