One of the greatest things about playing video games is the great sense of achievement when setting a new high score or beating a particularly difficult section. A good difficulty curve will leave the player feeling
challenged without getting frustrated. The most common way of managing this difficulty progression is to divide a game into sections separated by increasingly difficult boss fights. Beating the final boss means you beat the game, an nothing is more satisfying than finally besting a final boss that have vexed you for weeks or maybe even months.