It keeps me intellectually stimulated.

John: This new project is really challenging, but in a good way.

Alice: I can see that. It keeps me intellectually stimulated, and that's what makes it so rewarding.

John: Exactly! Sometimes I feel overwhelmed, but then I realize it keeps me intellectually stimulated and that's what matters.

Alice: That's a great attitude to have. It's good to find challenges that keep your mind engaged.