Why do Orthodox Christians talk so much about guarding your thoughts?

Do I really need two more Oreo cookies after I just ate four of them? The answer to that is yes. But for some people, the answer should be no. We all have our own things that get us, that hook us. But it always begins with the thoughts. There's a beautiful book by Elder Thaddeus that I recommend for everybody as part of our catechumen reading, called Our Thoughts Determine Our Lives. Even that small saying is enough to understand it: everything in our life, the good, the bad, and everything in between, begins in the mind with the life of the thoughts.