I'm not sure I follow what you mean. But, you can trace inductively how sellers of goods and services start to amass wealth, because prices are set by what buyers see as worthwhile rather than at a minimized "cost plus" basis.

And eventually, once you have enough capital, your new job becomes managing your capital instead of whatever you did before. There's two ways to look at that. Your labor is research and planning of your own investments. Alternatively, you are "selling" capital to others who are seeking investments, and they are "buying" it with labor. But the same story as above holds true. The price of capital (in terms of labor) becomes what the market will bear rather than a minimized "cost plus" pricing.

This duality is what it means for labor and capital to be fungible, right?