Lolwut?!? This is nonsense. GTFO.
SIMPLE EXAMPLE:
Company X has 1,000,000 shares on issue.
There are 100 shareholders owning 10,000 shares each.
Current share price is $10. Market cap is $10 million. Each shareholder with 1,000 shares has $100k worth of shares.
1 person sells their 1,000 shareholding to a new investor, at a price of $11 per share.
After transaction with the share price at $11: market cap is $11 million. Each shareholder with 1,000 shares has $110k worth of shares.
$1 million worth of market cap has been added, no one has lost any money.
Even using the absurd notion of foregone gains by those that sold, the person who sold at $11 has lost precisely zero dollars, while the other 999 shareholders have gained $10,000 each.
lets say the next sale is at $22 per share. The market cap increases by $11 million to $22 million, and 999 shareholders gain $110k in the value of their holding. The one person who sold at $11 has missed out on that $110k in upside gains, but that is 1 person missing out on 110k vs 999 people up 110k each.
In no way is that a zero sum game.
There is a reason the Weapon of Mass Wealth Creation known as the stockmarket is one of the best inventions ever.