Be careful. Maybe it's a useful rule of thumb, but be careful of the "searching for your keys under the light pole" problem.

I worked at Google on rich content indexing for 4 years, more than a decade ago now. Google is pretty good. It used to really cater to "long tail" searches, but a combination of SEOs getting better (and specifically targeting Google) and "learn to rank" over-optimizing for the median query, means that lots of long-tail queries don't do very well on Google.