This article discusses how scientists have traditionally divided fungi into clear categories of disease-causing pathogens versus harmless non-pathogens, often based on studying just one strain. Recent research shows that non-pathogenic fungi can actually have many disease-causing traits similar to pathogenic species, suggesting the boundary between dangerous and safe fungi is not as clear-cut as previously thought. By studying many different strains across species, researchers can better understand how fungal diseases develop and potentially evolve.