I've been building niche sites for over a decade, and there's one mistake that looks harmless at first but quietly undermines everything: writing for search engines instead of for people. It feels fine for months-traffic trickles in, rankings hold up. Then one day the plateau hits, engagement drops, and you're left wondering where it all went wrong. Most teams don't see it coming until the traffic starts dying.
The other big one is ignoring SEO from the start. You create a pile of content that reads well, but nobody can find it through search. By the time you realise the error, you've got a hundred posts needing a complete rework. It's like building a house on sand-looks solid until the first storm.
Inconsistent voice across different pieces is another sneaky killer. Seems minor, but after a few months your brand sounds like five different people wrote it. Your audience gets confused about who you actually are. These mistakes compound slowly, like interest on a bad loan. Avoid them early, or pay the price later.