You get rewarded significantly less if you upvote an item later. Early upvoters are highly rewarded. Your upvote rewards are basically proportional to 1/x where X is 1 if you were first to upvote, 2 if you were second, and so on.
how early they upvoted the content relative other users
1/xwhere X is 1 if you were first to upvote, 2 if you were second, and so on.