What feature makes a quiz app truly addictive (in a good way)?

I've been building a quiz and trivia app over the past few months, and one thing I've realized is that creating questions is only half the challenge. Keeping users engaged day after day is much harder.

Many quiz apps rely on daily rewards, streaks, leaderboards, XP systems, or achievements. Others focus on multiplayer, user-generated quizzes, or personalized learning. Each approach seems to work for different audiences.

I'm curious about what actually keeps people coming back.

If you've used or built a quiz, educational, or casual game:

• What feature made you open it again the next day?

• Do you prefer competing on leaderboards or simply tracking your own progress?

• Are daily challenges and streaks motivating, or do they become repetitive?

• Have you ever created your own quizzes? If so, what made that experience enjoyable or frustrating?

For my app, I'm experimenting with a combination of a quiz creator, weekly challenges, XP progression, achievements, and community-created quizzes. I'm trying to balance learning with gameplay without making it feel overly gamified.

I'd love to hear your experiences—whether you're a maker, educator, or someone who enjoys trivia. What has worked well, and what would you avoid if you were designing a quiz app today?