It Just Doesn't Make Sense

Why, why is a Serrano so much spicier to me than a Habanero is? A whole Habanero isn't even as spicy to me as one 25th or so of a Serrano. Now, I have recently bought six or so various hot chiles. Ghost Peppers I did not bring with me, simply because they are unnecessarily hot, and also because they're kind of expensive. Although, I must admit, they are probably delicious once diluted in a mixture or substance. My favorite chilies include Cayenne, Jalapeno, . I think Habanero's pretty good although I think the previous chilies are probably way better, at least that's what I think so far. I can eat a Habanero as if it were a dash of mild hot sauce...literally! I also like the taste of Kung Pao. How is it possible for a freaking Habanero to be less potent than a Serrano?! Seriously, how?! Does it have to do no just with heat? Just compare them on a heat scale. It just doesn't make sense? Are my senses simply screwed up?!