"No!" Kagan exclaims. "Every behavior has more than one cause. Don't ever forget that! For every child who's slow to warm up, yes, there will be statistically more high-reactives, but you can be slow to warm up because of how you spent the first three and a half years of your life! When writers and journalists talk, they want to see a one-to-one relationship--one behavior, one cause. But it's really important that you see, for behaviors like slow-to-warm-up, shyness, impulsivity, there are many routes to that."