那是个无心的错误。

It was an ___innocent mistake.

那是个无意的评论，我不是想伤害他的感情。

It was an ___innocent comment, I didn't mean to hurt his feelings.

一时冲动，我建议他试试，正是这让一个无意的事件变成了一场噩梦。

On the spur of the moment, I advised him to try it and that's what turned an ___innocent episode into a nightmare.