What is Keyword Difficulty?
Keyword Difficulty is a metric that shows how much competition a keyword has. The quantitative signal is relative to the niche state, and you can find it in various SEO research tools, like Ahrefs or Ubersuggest. To note that modern SEO works with topics and not exact keywords like in the old days, still, a lot of professionals use it, and clients wrap their minds around it so that I will say a couple of words.
If you accept the logic of the metric system, you can expect that elevated keyword difficulty, makes the keyword more competitive and harder to rank for. For a domain with no strong background in SEO, professionals tend to start with the medium to low competition keywords, or even long-tail to exploit hidden opportunities. My approach is different. I like targeting topics that will bring the most traffic and not just keywords. So, I write about a theme and provide as much information I can about it; not the other way around, taking a keyword and try to make the text around it make sense.