You can give the answer to this question in your sleep.
The mission. The vision. The contribution to the field, the industry, the community. The legacy. The version of the answer that you give in speeches, in interviews, in the conversations with your team about why this matters. It is not false — every word of it is something you genuinely believe. It is also, in part, a construction.
Peter Drucker asked the question as a management principle: what is our business, who is our customer, what does the customer consider value? Simple, apparently. In practice, the honest answer to Drucker's question — not the mission statement but the actual current behaviour of the organisation — reveals what is actually being built, which is often different from what the stated mission describes.
The same question applied to an individual life has the same gap between the stated answer and the observable answer. What is being built, actually? Not in the mission statement of the life but in the allocation of time, attention, energy, and care that constitutes the life's actual daily investment. The observable answer to that question is different from the stated answer for most serious people — not because they are dishonest but because the stated answer is what the life is supposed to be about, and the observable answer is what the life's actual momentum is producing.
The Brihadaranyaka Upanishad's Yajnavalkya, preparing to leave his household and enter the final stage of life, tells his wife Maitreyi: the husband is not dear for the sake of the husband — the Self is dear, and the husband is dear for the sake of the Self. This is not coldness. It is the Upanishadic instruction to examine, with honesty, what anything is actually for. Not what it is supposed to be for. What it is actually for — in the structure of your desire, in the genuine orientation of your energy, in the thing that would be missing if it were absent. The examination is uncomfortable. It is also the only examination that produces genuine clarity about what the remaining time and energy should be directed toward.
Drucker's second observation is equally precise: the most important decisions are not about what to do. They are about what to stop doing. The life that is genuinely oriented toward what matters requires the removal of what is consuming time and energy in service of what the life was supposed to be about rather than what it is actually about.
What are you actually building? Not the answer that serves the narrative — the answer that the honest observation of the last twelve months of your daily life produces. And is that building genuinely for the reasons that justify the cost it is extracting?