Why are some people good at algebra and bad at geometry and vice versa? I've met people who say they did very well in algebra but were terrible at geometry in high school and some people who say they did very well in geometry but were terrible at algebra in high school.

I'm curious if people who do well in geometry are right-brained thinkers while people who do well in algebra are left-brained thinkers? Why is there a difference in ability, when algebra and geometry are just branches of the same subject, mathematics?
In short, algebra and geometry are different type of cognitive abilities. Geometry is more spatial and algebra more verbal-logic.

Kestenbaum, C., Williams, T. D., Handbook of Clinical Assessment of Children and Adolescents, NYU Press, 1988.