别因为你知道秘密，就自作主张。

You must not take liberties because you are in the secret.

他自作主张承担起保护她的责任。

He took upon himself the responsibility for protecting her.

我不喜欢你这种擅自使用我的自行车的自作主张的行为。

I don't like the cool way you used my bicycle without my permission.

不要因为是小事就不禀告父母而自作主张去做，那就不合为人子女的道理了。

If you act just as you please, then you've not been a dutiful child.

班里诸多缺席者常常是刻意回避那些无聊的讲座，我却不敢自作主张的免除听课的责任。

Unlike many absentees in my class who often abstained from attending the boring lectures, I dare not absolve myself from this responsibility.