Strictly speaking, WEIRD is a problematic phenomenon in experimentation and statistics because most research in psychology because is based on underrepresented samples of college students from the United States and Europe.
They found that people from Western, educated, industrialized, rich and democratic (WEIRD) societies — who represent as much as 80 percent of study participants, but only 12 percent of the world's population — are not only unrepresentative of humans as a species, but on many measures they're outliers.
Culture influences psychological processes. Individual thoughts and actions influence cultural norms and practices as they evolve over time, and these cultural norms and practices influence the thoughts and actions of individuals.
According to the textbook, the problem with "weird" samples is that they are NOT: very easy to measure.