1. i've made a tough decision,sir. here is my resignation.
我做了个艰难的决定，这是我的辞呈。

2. i quit because i don't want to be stuck in a rut. i want to move on.
我不想陷入窠臼所以才辞职。我希望能向前迈进。

3. first of all, i'd like to say that i've really enjoyed working with you. however, i think it's about time for me to leave.
首先，我要说的是，我真的很高兴能和你一起共事。但是，我觉得该是我离开的时候了。

4.i've been trying, but i don't think i'm up to this job.
我一直很努力，但是我觉得自己无法胜任这个工作。

5. i've been here for too long. i want to change my environment.
我在这儿待得太久了，我想换一下环境。

6. i'm sorry to bring up resignation at this moment, but i've decided to study abroad.
很抱歉在这个时候提出辞呈，但是我已经决定出国念书了

7. to be honest, i've got a better offer.
老实说，我有一个更好的工作机会。

8. i'm running out of steam. i need to take a break.
我精疲力竭了，我要好好休息。

9. i'm quitting because i want to try something different.
我辞职是因为我想尝试不一样的东西。

10. i want to expand my horizons, so i've put in my notice.
我想拓展自己的视野，所以我辞职了。