The three-circle niche test
The most reliable way to evaluate a niche is to draw three overlapping circles: (1) what you know deeply or have genuine experience with, (2) what people actually search for and need help with, and (3) what has real monetization potential — affiliate programs, products, or advertisers in the space.
A niche that hits all three circles is worth building. A niche that hits only two will struggle in a predictable way: strong knowledge + strong demand but no monetization means you will work hard for almost nothing; strong knowledge + strong monetization but no real demand means you are writing for an audience that does not exist yet; strong demand + strong monetization but no genuine knowledge means your content will feel thin and competitors with real expertise will outrank you.
The same broad interest can be positioned as a strong or a weak niche depending on how you frame it. "Health and wellness" is a weak niche — too broad, dominated by massive publications. "Evidence-based recovery nutrition for amateur endurance athletes" is a strong niche — specific audience, clear search intent, and strong affiliate potential from sports nutrition brands. The knowledge you bring is the same; the positioning determines whether you can own it.