Common factors are ubiquitous. First, we show that, however in vision, correlations of performance in similar paradigms are low even though test-retest reliability is high. Second, one might expect that correlations increase with increasing age because of the common factor of age. However, this is not true. Third, we found significant correlations between the Ebbinghaus and Ponzo illusion, but this relationship was the only significant correlation out of all 16 comparisons. Surprisingly, we found a significant link between the Ponzo illusion and both mental imagery and cognitive disorganization. Almost all other correlations between illusions and personality were not significant. Fourth, we found high correlations between 19 versions of the Ebbinghaus illusion, suggesting that there are extremely specific factors. Beyond these factors, vision is highly individual except for rare common causes, which unfold in a complex space and do not easily map on common explanations in vision.