By far the biggest setback I've faced when building an online business is spreading focus too thin. Information is plentiful online, and as a result of this, it's easy to spread your focus on several opportunities at once without truly committing to one thing. This can lead to a lot of projects that get started but never finished, which reduces effectiveness. The most effective way I've found to overcome this is to set rules for myself about what content I'll interact with and what content I'll simply ignore. By narrowing my focus, I get more done where it matters and spend less time on distractions and vanity metrics that don't drive results. The #1 lesson others can learn from this experience is that singular focus really, truly matters. It's the ultimate cliche, but saying "no" more often, including to yourself when you feel distracted, is by far the most powerful way to improve your ability to grow your business and make money effectively.
One of my biggest setbacks was launching a niche blog that didn't get traffic for months. I went in with lots of enthusiasm and put huge amounts of work into my content, then realized I hadn't done any meaningful keyword research and as such, wasn't reaching anyone. I paused, learned SEO basics, and rewrote a lot of my content with search intent in mind. Traffic slowly grew after that and our company's blog is now our top source of inbound leads. The key lesson others can learn from this, and one I often remind myself of, is to research and aim before you shoot. When you know what people are searching for before you start writing, you are in a much more powerful position to reach and influence them.