鱼不知深浅
[yú bù zhī shēn qiăn]
'Fish Not Knowing Depth' may imply living in blissful ignorance like a fish swimming without concerning how deep the water is, or it can mean someone doing things rashly and recklessly like the inexperienced fish which doesn't measure risk well, depending on the context and tone conveyed when creating such an elegant metaphor using animals from nature and their characteristics.