What makes me sad

Humans are emotional,for me.I think I am a quite cheerful person that always bring joys to others but sometime things happened in my life which makes me sad too.
When I was still in kindergarten, I get sad easily over even the smallest thing.Friends ignored me,classmates snatch my toys away and when the time I did not get what i want.I will just cry out loud to show that I was sad.People may think that was childish but in that age of me,cry was the only way to express myself that I was sad.
In primary school,when I became more thoughtful and sensible to things around me.I will learn to control myself from expressing my sadness but sometime I will just burst out my cry when things really getting worse.I still remember that was a time,some of my classmates were teasing at me just because I am a foreigner, they started laughing at my pronunciation and when I tried to ignore them,they began to laugh at my parents and do childish stuff just to make me angry. At that moment, I really felt sad and tears began to shed down."Why can"t I had a fair treatment as a foreigner?" I shouted at them and that was the first time i cried in primary school.
Now,I was in secondary two,growing up as a teenage and not only became more thoughtful but also became mature in my thinking. I thought this would makes me more happy but it was not true, I start to realize that the world was in danger, deforestation and all the air,water pollution had caused global warming. All of this were causing by the human' action and leads the world to damage. These facts really hurts me and I was sad about it and not only the damage of the earth had makes me sad. The school word,project work and all the exam that I am facing also brought me quite a lot of stress, though sometime it really makes me frustrated but I will also treat it as a motivation for me to achieve my goal and things that I desire for.
Although this things makes me sad but i feel that a human's emotion cannot just be happy but we also needs sadness to balance our feeling and express to others what we really feels.