Thank you so much ^^, but I want to know Why we have to use past simple tense and past perfect tense in this sentence "Personally, I felt that it was quite easy because I had wanted to become a teacher ever since I was little."
Usually when you are telling a story, you use past tense. But we can change it present tense if you want to.
Past perfect tense is used for something that happened before the simple past tense. The "tôi muốn thành giáo viên" part happened in your childhood, so it happened before the "tôi cảm thấy việc đó dễ dàng" part, which happened more recently.