Don't Hold Back Too Long on the Carrots
Besides information, you need to give the player incentives. There is a wide variety of rewards that past games have offered players, and that future game designers will dream up.
These rewards include an expansion of abilities, weapons, and defenses. They can also include treating the player to intriguing pre-rendered cinematics.
There's a piece of street wisdom often repeated that a game should, early on, provide the player with lots of quick successes to get him or her excited about the game. After that, as the common wisdom goes, rewards should come less frequently, and be much harder to earn.
It's true that in games and in life, you want to take on progressively harder challenges. A player usually expects to and wants to get clobbered or killed by the game's biggest boss numerous times before finally being victorious.
But there's a danger if the game designer takes the player's willingness to continue through a game for granted.
Many game companies rely on extensive testing of their games to see where "good frustration" ends and "bad frustration" begins.
But in some games, the problem persists. Don't be overly stingy on giving the player those carrots.
A related issue is that not every enemy needs to be difficult to conquer near the end. You can throw in some fodder. The player has worked hard to build up skills, weapons, and defenses. Let him or her enjoy clobbering some baddies with his or her hard-won fighting skills.