This phrase describes a breadth of mind that is broad and open as a deep and expansive mountain valley. Metaphorically, it refers to a person who is modest, generous, and tolerant, good at listening to other people’s opinions and taking them into consideration, which is a desirable characteristic deemed typical in eminent people and leaders. People with such a quality can accommodate various opinions, including criticism and objections. In so doing, they can make timely correction of their mistakes or amend erroneous policies, thereby attracting more people to join and support them. This term is similar in meaning to other concepts such as “having ample virtue and carrying all things” and “a broad mind achieves greatness.”

In ancient times, a person who is good at practicing dao was seen as exquisitely insightful, magically capable, profoundly knowledgeable, and beyond the understanding of ordinary people… He looks simple and natural as a piece of uncarved wood; he is open and broad as a tranquil valley. Laozi

A broad-minded person who treats others with respect has no problem attracting people eager and willing to follow him. History as a Mirror

He has an open mind as broad as a valley, which explains why he becomes increasingly better in poetic accomplishments. Yuan Mei: Addendum to Suiyuan Remarks on Poetry