不知深浅 Without knowing the depth
Explanation
比喻对事情的严重性或难易程度缺乏了解，做事没有分寸。
It is used to describe someone who lacks understanding of the seriousness or difficulty of a matter, and does things without discretion.
Origin Story
唐僧师徒西天取经，路遇一妖怪，自称莲花洞主。孙悟空不知深浅，擅自前往挑战，结果被妖怪打得落荒而逃，幸亏有观音菩萨相助才化险为夷。后来，孙悟空吸取教训，细查妖怪底细，最终将其制服。这个故事告诉我们，做事前要先了解情况，切勿盲目行动。
On their pilgrimage to the West, Tang Sanzang and his disciples encountered a demon who claimed to be the master of Lotus Cave. Sun Wukong, without knowing the depth and shallowness, rashly went to challenge him. He was defeated and barely escaped. It was only with Guanyin Bodhisattva's help that he survived. Later, Sun Wukong learned from his lesson, investigated the demon thoroughly, and finally subdued him. This story reminds us to understand the situation fully before acting and avoid reckless behavior.
Usage
形容人做事欠考虑，不顾后果。
It describes someone who acts carelessly without considering the consequences.
Examples
-
他做事不知深浅，总是冲动行事。
ta zuoshi buzhi shenqian, zongshi chongdong xing shi.
He acts without knowing the depth and shallowness of things, always acting impulsively.
-
小明不知深浅地挑战高手，结果输得很惨。
xiaoming buzhi shenqian de tiaozhan gaoshou, jieguo shu de hen can
Xiaoming challenged a master without knowing his own capabilities, and ended up losing badly.