But I still wonder

Trees are tall 

But sometimes they fall 

Their trunks are round

And they stay on the ground 

Birds fly high 

Sometimes they fight 

Babies stay in the nest 

But make such a pest

Mountains are thick 

Cousins to bricks 

Sometimes they’re snowy

Sometimes they wow me 

What makes trees tall? 

And why do they fall?

Why do birds fly? 

And why do they fight?

Why are mountains thick?

And change to a brick? 

Science already answered these questions but I still wonder 

Why does it need to happen?