Dan it doesn't have to be a zero sum game. In your example, what...

Dan it doesn't have to be a zero sum game. In your example, what if the seller at $1.00 had bought at 50 cents - they are happy cos they've made a 50 cent profit.
You as the buyer at $1.00 then sell at $2.00, so you, too, are happy cos you've made a profit.
The zero sum game really only eventuates if the company/asset never really increases/decreases in value over time. If the company/asset DOES increase in value, then all shareholders, past and present, can share in the win...can't they?
I have no problem leaving something on the table for the next shareholder - that doesn't mean I've lost.