What is Your Motivation?

I am having such a hard time getting back into the swing of fasting. I cant stay focused or motivated for more than a day and a half. I start off strong, but dinner always gets me. I recently(2 weeks ago) went as long as 4 days, but ended up ending the fast because I was offered a Subway sub and I rarely get to eat there...so I caved. Its been very hard to go back to fasting since that happened, even though I really want to and desperately need to. So tell me, fellow fasters...what keeps you motivated to go on a long fast?