Chinese to English Social Sciences Education / Pedagogy

一個有信心的人，做事一定有成就.
My translation: A person who is confident must be a successful one. 做事 in the sentence doesn't have to be translated into "in his work," because "succeed" already implies that. And the confidence in the sentence is not limited to work only. We can understand that the people are confident themselves. So it's needless to back up 'confident' with 'in his work.'

I prefer to translate 有成就 into "be a successful one." 成就 is different from "success" in English. While success is a general common word in English, 成就 denotes the level or degree of one success or a series of successes, such as during a lifetime, or a standout one that is set against average conditions or that is contributive to people. It's illogical "a person who is confident in his work will ALWAYS succeed," but it's right he is a successful one in some way or to some extent.

一個人 can be viewed as a phrase in which 人 is modified by 一個。個 is a qualifier just like "piece" in "a piece of paper." 一個人 literally means a person. But sometimes it goes beyond that meaning. Compare the following two sentences:
* 我看见一个人急匆匆走过。I saw a man pass by in a hurry.
* 一个人，必须学会思考。A human must learn how to think.

成功 is more common to 成就, as success is to feat or accomplishment sometimes. 成就 does act as a verb sometimes, such as in 成就一番事业, which form has its root in ancient Chinese. But it's rare in plain writing.