To make a successful product solo, you need many skills that may not intersect.

Product (design and strategy)

Engineering (most cracked passer of everything)

Business (most of us don’t know this and fail woefully at it)

Marketing (the most difficult side of building a product)

User experience (it intersects with product and marketing and is the only way to retain users or get them past onboarding)

Finance (the most debilitating part: if you can’t raise and manage funds, your product wouldn’t exist)