Read the following article and answer the question.

Earlier today during PE I jumped off the stairs about 1 - 2 meters and slipped towards the end of the stairs landing on my right elbow , right knee and hip . Nowabout 10 hours later my shin has a small bruise / lump on it and it hurts to walk . Applying pressure to it stings a little and I was walking a moment ago and fell to the floor because of a sudden pain in my right hip .

Why may the narrator have injured themselves ?
They did n't take exercise seriously .