Ser vs. Estar

The Spanish language has two verbs that mean "to be."  To generalize, estar is used to indicate location or a temporary state.

John está en el cuarto de baño, probablemente el juego de Riesgo en su iPhone.
John is in the bathroom, probably playing Risk on his iPhone.

Ser is used (again, generally) when describing a more permanent state of being, such as physical attributes or personality traits.

John es una locura de Taco Bell, aunque él sabe que es casi lo peor que puede poner en su cuerpo.
John is crazy for Taco Bell, even though he knows it's pretty much the worst thing that you can put in your body.

This differentiation between a temporary and permanent "to be" verb becomes especially interesting to me in the context of trying to change onself.  There are certain things I've been terrible at for my whole life to date, but I hate to think that they will plague me until the end of my days.

For example, I am a Nail Biter (yes, capital N, capital B).  Always have been, probably always will be.  While I had braces for three years I completely stopped, and when they were removed I picked up right where I left off.  Yet, nearly every day that I catch myself indulging in this habit, I say to myself, "Enough!  This is it, no more nail biting FOR THE REST OF MY LIFE, starting right now."

I usually break this pledge within five minutes.  Then re-make it five minutes after that.

Still, I can occasionally claim a victory against myself.  Two months ago, I joined a gym and told myself that I'd never let that bully at the beach kick sand in my face again.  Since then, thanks to my weightlifting regimen, I've gained 10 pounds - which may not sound like much to you, but is actually a Herculean accomplishment given my physique.  Sure, only some of that weight can be attributed to muscle gain while the rest comes from a nascent belly paunch and my relentlessly growing mop of hair; it feels good to know that I'm capable of demonstrating the discipline required to institute a positive change in my life.

John es un perezoso por lo general una criatura de la costumbre, aunque de vez en cuando le va a sorprender a sí mismo.
John is a usually a lazy creature of habit, though occasionally he will surprise himself.