From my point of view, challenge is everything beyond our abilities or that we want to do but never tried before. For example, it was a challenge for me to talk to strangers several years ago because I was very shy and hadn't even asked a stranger for directions. But after I did it for the first time, it was not a challenge for me anymore because I had overcome the fear and considered it as a normal thing. When I entered my university, it was a challenge for me to speak and show myself to the public. And I remember I was shaking my legs behind the platform while reciting a message in front of my classmates and my teacher for the first time. Fortunately, I often took those challenges actively to overcome them, so I could speak and show myself to the public soon.