The most common question from aspiring authors is the wrong one: “What should I write about?” The better one is: “What is being searched for that nobody answers well yet?” A niche isn’t a topic you like — it’s the intersection of demand, gap and your competence.
The three circles
Think in three overlapping circles. The first is demand: are enough people searching for it? The second is competition: is the field already crowded or surprisingly open? The third is your authority: can you write about it credibly? Only where all three overlap lies a real niche.
Demand without competence → you get found out
Competence without demand → nobody reads it
Demand without a gap → you disappear in the field
All three → your niche
A good niche is narrow enough to own and large enough to live on.
Narrower is usually better
“Productivity” isn’t a book, it’s a library full of competition. “Productivity for shift workers in healthcare” is a niche — specific enough that the audience instantly feels addressed, and open enough that you rank. The fear of reaching too few almost always leads to aiming too broad and hitting no one.
Validate, don’t fall in love
The most dangerous niche is the one you fell in love with before you checked it. Data is your friend here: it soberly shows whether your favorite topic has a market. Sometimes the most honest answer is no — and the second-best idea is the one that actually finds readers.