That's the only reason anyone does anything for you.

That's the only reason anyone does anything for you. (that's the only reason anyone does anything for you)

意思：

👉 那就是别人愿意为你做任何事的唯一原因。

结合语气，也可以翻译成：

👉 别人之所以愿意帮你，唯一的原因就是这个。

重点：the only reason

the reason = 原因

the only reason = 唯一的原因

例如：

That's the only reason I came.
那就是我来这里的唯一原因。

anyone does anything for you

这一部分很容易让人迷惑。

anyone = 任何人 / 别人

do something for someone
= 为某人做某事 / 帮某人

所以：

anyone does anything for you

= 别人为你做任何事情

这里 anyone 和 anything 都是在一个泛指的范围里：

anyone = 不管是谁
anything = 不管什么事情

所以整句：

That's the only reason anyone does anything for you.

字面：

那是任何人为你做任何事情的唯一原因。

自然翻译：

那就是别人愿意为你做事的唯一原因。

一个很重要的结构

the reason + someone + does something

例如：

That's the reason I called you.
这就是我给你打电话的原因。

而：

That's the only reason anyone does anything for you.

加上 only 后，语气就非常强：

“别人对你好，并不是因为你值得，而仅仅是因为这个。”

所以如果这是你正在看的剧情中的台词，语气可能带有责备、讽刺甚至攻击性。