When we were kids, we always wanted to do one thing and we'd believed that we could be the best. That's why we tried so hard! 可以幫我更正文法嗎?

When we were (過去年幼時，過去式O) kids, we always wanted(過去的希望，過去式O) to do (帶to不定詞，O) one thing and we'd believed (過去一段期間一直認為，過去完成式O) that we could (當時可以作到，過去式O) be the best. That's (今天對過去之回顧，這是一個歷史與事實，用現在式O) why we tried(當時的努力，過去式O) so hard!

問題該是 – 何謂 to do one thing - 特別的一件事? 青春期的幻想嗎?
還是寫的不要讓大家猜想較好
When we were kids we always thought we could do anything and did it best, that’s why we tried so hard!

When we were kids, we "were" constantly bent/總是執意 on something (had been constantly bent 文法上我覺得本身沒問題，但感覺上意思被綁住在 – 持續的特定事情了), and we had always believed that we could be the best.
另bent on 的使用，幾個字典說法不一，中文的意思為非常執意(Longman 認為大都用在不好的事，其他字典倒未必如此行容，were bent to如改為were determined to，執意 就變成較正面的決心 – 其實我也很少看文法 –不知有沒有講錯，實在也不是很有把握，你英文程度已非常好) 。
From Longman Dictionary of Contemporary English
bent on something
completely determined to do something, especially something bad
a crowd of hooligans bent on violence – 小混混執意暴力
be bent on doing something
They seemed bent on destroying his career. – 他們執意破壞汽車

From Yahoo Dictionary
1. 決心採取(某行動), 專心致志於(做)某事
be bent on pleasure, mischief, etc. 一心要享樂、搗鬼等
He is bent on winning at all costs. 他決心不惜一切去爭取勝利。

劍橋字典
be bent on sth/doing sth
to be determined to do or have something:
He was bent on getting married as soon as possible.

其他英文網站資料
1.Just look around, it won't last forever, man has been bent on (負面事物) destroying it as fast as we can. The Messiah will come before they destroy it all.
2. Since the 60's society has been bent on (負面事物)rebelling against authority.
3. For a while, she had been bent on becoming a writer. But writing was boring.

補充：經國外網站詢問，bent on 也可用於正面事物描述

Error and correction in Tenses Only in your heading of your article in a posting question ?
When we were kids---past tense of "be"
we always (be) wanted---vt, vi, require----linking v. indicating a change from one quality, place, etc. to another=Kids want to be;
to do one thing
and we'd believe----->vt, vi, .feel sure ; be of the opinion (that)
that we could be the best---->.past tense of can ; used in indirect speech in place of can if the main verb is past tense to express conditions, and to express occasional occurence and inclination.can--->could.
That's why we (have) tried----->perfect in the performance of kids' duties----perfect tense composed of have +pp.----->present perfect tense;
so hard (for the endeavour,the effort, the attempt )

When we were kids and always wanted to do things to the best of our abilities; that's why we tried so hard. Yip

When we were kids,we always wanted to do one thing and we'd believe that we could be the best. That was why we
tried so hard!