Focus on what you HAVE achieved, instead of what you have left to go. And remind yourself of all the other amazing benefits of doing it - these will be different for each person. Maybe try a gratitude diary each day - even just a few notes in your phone. You got this!
For me what motivates me a lot is knowing the fact I’ve failed so many times and how much that upsets me. I tell myself that I can’t give in or be disappointed because I’m more content about how my body is today then it was a week ago.