I want to expand my horizons.

    我想展我的视野。

    I've made a tough decision， sir. Here is my resignation.

    长官，我做了一个很困难的决定。这是我的辞呈。

    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。

    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，我真的很高兴能与你共事。但是，我觉得该是我离开的
时候了。

    I've been trying， but I don't think I'm up to this job.

    我一直很努力，但我觉得无法胜任这个工作。

    I've been here for too long. I want to change my environment.

    我在这里待太久了。我想转换一下环境。

    I'm sorry to bring up my resignation at this moment ， but I've decided
to study abroad.

    我很抱歉在这个时候提出辞呈，但我已经决定要出国念书了。

    To be honest， I've got a better offer.

    老实说，我有一个更好的工作机会。

    I'm running out of steam. I need to take a break.

    我精疲力竭了。我需要好好休息。

    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。