In anime watching communities, it is common for many people to adopt what I consider to be relatively negative habits: the “four episode test” (and some variations) and watching a show to completion despite it already performing below expectations.
I really resonate with How to Recognize a Terrible Anime (in just one episode) from Trixie (nee. Digibro), and I recommend and endorse the following set of ground rules:
Generally speaking, people evaluate anime on scales of 1-10 for arbitrary reasons. I usually only complete shows 7 or higher unless there are other circumstances. When a show falls lower later, it's harder to know and I finish shows that are “almost done” if I believe they can be saved.
Don't waste your time watching junk! Watch good stuff instead!