Whether it is true or not that in markets like Bitcoin (crypto) ; one person gains only when the other losses some thing. Suppose one person bought one Bitcoin for $5000 in January 2017 and sells in June 2017 for suppose $10000 he gains $5000 by selling. Now the purchaser in June 2017 @ $10000 sells it for $6000 in January 2018 and as a result he losses $4000. So it is clear from the example that the profit of seller in June which was $5000 includes the loss suffered by the person who bought it in June 2017 and sold in January 2018.
If there are some other reasons for this profit / loss factor, I request other members to please share their knowledge with the platform because my opinion may be on the basis of partial truth and there may be other factors responsible too.
You are partially right but those who bought what someone sold can still profit in the future. The full truth is that, the Bitcoin is being passed from one user to another using a process called trading, which have two categories, the buy and selling. Bitcoin is being passed from the seller to the buyer and then the buyer later on can become the seller to pass it on to another person. The buyer can profit if he/she can sell it at a higher price.
Of course they can profit in the future, but only provided there is a an influx of fresh money into the system. At some point in the future there is no more people to sell to, you are the last holder of bitcoin and you must sell cheaper than you bought or you will not sell at all. At that point in the future bitcoin may be 20k or 100k or 1m, I do not know, the point is that you will kind-of pay for the money other guys before you have won.
You guys are discussing only about the trading of bitcoin.
You are completely ignoring the value that it derives from being used for (edit)
buying other cryptos, having the most underlying infrastructure and having the most information and support out there for anyone who seriously wants to explore crypto.
The underlying value it derives from driving the crowdfunding requirements of so many startups and future companies is also being largely ignored.
Thats what gives it value and not just the people buying in for trading purposes or for getting rich quickly.