Hans eysenck thought that personality differences result from

I believe the answer is: biological differences that create variations in personality traits from person to person

Hans eyseck believed that our tendency to behave a certain way is influenced by the genetic composition that written in our DNA.
Eyseck's theory does not consider how the environment could be a huge factor in influencing people's behavior and personalities. 

White dwarf is very hot, but also very small and that is why it may appear dim.