Why is weight loss a Roller Coaster?

When it comes to weight loss it has been a roller coaster ride for me that never ends. I have successfully lost weight many times, but it’s the keeping up with the healthy habits that seem to be the problem.
The other day I was at the grocery store getting ready to leave and I saw a women I new who had lost a good amount of weight doing WW. As I passed her by all I could think is good for her she still looks great, but how does she do it. What makes weight loss stick for some and not me. Did they have a ahh moment or is it just easy for them to keep the weight off. Do I have a unstable metabolism that makes it easy for me to gain? What is the secret?
I don’t know if I will ever find the answers to these questions, but I am willing to try.
I have decided to be very strick with writing down my food choices and my feelings when I eat to see if somehow I can figure myself out.
Maybe I will discover something I haven’t in the past.