发傻劲儿

do something stupid

看你那傻劲儿，这么大的人了，做事还跟孩子似的。

You're so foolish. You're all grown up now but you still behave like a child.

这人还真有点儿傻劲儿，一人就抱起那么大的石头。

This person is really going for it, picking up such a big rock on their own like that.

光靠傻劲儿蛮干是不行的，得找窍门。

It's not enough to rely on enthusiasm alone: one must find the knack.