The difference in the ratings between two players serves as a predictor of the outcome of a match. If two players with equal ratings play against each other, they are expected to score an equal number of wins.[2] A player whose rating is 100 points greater than his opponent's is expected to score 64%, if the difference is 200 points the expected score for the stronger player is 76%.[3]

A player's Elo rating is represented by a number, which increases or decreases based upon the outcome of games between rated players. After every game, the winning player takes points from the losing one. The total number of points gained or lost after a game is determined by the difference between the ratings of the winner and loser. In a game between a high-rated player and a low-rated player, the high-rated player is expected to score more points. If the high-rated player wins, only a few rating points will be taken from the low-rated player. However, if the lower rated player scores an upset win, many rating points will be transferred. The lower rated player will also gain a few points from the higher rated player in the event of a draw.

Originally Posted by ImmortalPig

This isn't my theory, it's how ELO works.

You won't up your elo by beating people of lower elo, it's different amounts for different elo - a 300 elo losing to a 200 is different to a rank 2000 losing to a rank 1900.