The real price of every thing, what every thing really costs to the man who wants to acquire it, is the toil and trouble of acquiring it. What everything is really worth to the man who has acquired it, and who wants to dispose of it or exchange it for something else, is the toil and trouble which it can save to himself, and which it can impose upon other people... But though labour be the real measure of the exchangeable value of all commodities, it is not that by which their value is commonly estimated... Every commodity, besides, is more frequently exchanged for, and thereby compared with, other commodities than with labour.

Which is why something you've worked for is more valuable than something that was given to you.