Willpower is a fleeting resource
I don't know if it is simply the human state, or a modern day issue, but I feel there is an epidemic of self destructive thought processing around. Countless times I am faced with a lovely person in clinic, calling themselves 'weak', 'pathetic' or <insert negative self hating word> because they have 'no willpower' and ate the cookies.
Ladies and gentlemen, I beg you; please understand that willpower has nothing to do with having a healthy-enough lifestyle. Willpower is a fleeting resource; it comes, it stays a little while and runs out - a bit like a firework. It feels great while it lasts, but not so good when it runs out. Believing willpower is the answer is born of our quickfix societal mentality.
The real truth is that a healthy lifestyle is built over time, and is based on learning from our more successful and less successful days. We use those days to help us build systems which help us to succeed, rather than expecting ourselves to be superhuman and resist a gorgeous cake in the office during the 3pm slump.
Yes, it is actually rather straightforward and made of hard work: We trip, we fall, we learn. We build systems and we don't wait till we feel inspired to make changes; we do it anyway because we have enough life experience to know that if we do not <insert health giving activity> we enter a spiral of negative feelings/actions.