100 people own 1 share each of a company at $1.00 a share: 100 shares times $1.00 = $100 market cap. Then a new person wants to buy a share from one of the exis

100 people own 1 share each of a company at $1.00 a share: 100 shares times $1.00 = $100 market cap. Then a new person wants to buy a share from one of the existing owners. The existing owner wants $1.10. Now the stock is worth $1.10 and the value of all 100 shares is $110. The person who sold their 1 share made 10 cents profit, but the remaining $9.90 of new market capitalization was created out of thin air and doesn't exist until those owners are able to sell their shares on the market.