Literally Just a Rant

So I have a mystery for you guys today. How does a vayne who get's fed 2 kills and 2 assists in the beginning of the game end up losing to a sivir? How does an Elise take out three top turrets, an inhib, and ultimately both nexus turrets (through super minions), then takes out elder dragon (by soloing it) and somehow the enemy team still wins.