You, your brief background that led you to this idea.
Your vision of the future by creating / growing this product or service.
The mission of the company which states how specifically your product/service will bring about that vision.
Your customer - the specific segment you will dominate. Target segments must be (thanks @, CRO of Gusto, for teaching me what good segmentation really means) i) gettable, winnable, keepable, and profitable, meaning viable to achieve company goals.
ii) actionable, meaning comprised of a population with actionable skews or consistent characteristics.
iii) sizable, different from competitors target segments, and durable for ~5 years, to maximize growth potential.