See https://news.ycombinator.com/item?id=9716430 https://news.ycombinator.com/item?id=9716430, particularly Freditup, the_af & my comment discussing Emily Greer

See https://news.ycombinator.com/item?id=9716430 https://news.ycombinator.com/item?id=9716430, particularly Freditup, the_af & my comment discussing Emily Greer's rationale that players "pay-to-win" with large sums in physical sports games. Also, https://badgeville.com/wiki/Game_Mechanics https://badgeville.com/wiki/Game_Mechanics for a list of "engagement mechanics"