So I let down my guard, drop my defences, down by my clothes.

我放下所有的戒备，放弃抵抗，毫无保留。

youdao

I knew it as well as anyone, but I momentarily let down my guard and exposed myself unnecessarily to a deadly virus.

我和其他人一样，对这一点十分清楚，但在那一刻我还是放弃了防御，把自己暴露在致命病毒面前。

youdao

I could recognize my teacher's voice, the person in the phone was my teacher's voice, so I let down my guard, and talked happily.

我能认出老师的声音，电话那头就是我老师的声音，所以我放低了防备，和他愉快地聊着。

youdao

Like many victims of intimate partner violence, my mother let her guard down.

FORBES: Murder: The Ticking Time Bomb in Domestic Violence Cases