I'm not a repeated loser - I was fat for years and when I was ready to make a change, I kept at it. That was four years ago be I haven't quit yet! That said, though I didn't quit and try again I have learned a TON about what does and doesn't work for my body and life during this journey.
For me - conventional diet wisdom is crap.
Accountability with my food intake is key.
Scales are useful but not crucial.
I can't ever expect to eat like a never-obese person and not end up looking like I did formerly.
There is NO end date to my diet, it's for life.
Exercise needs to be smart, not hard, for the best results and long term adherence.
Low carb, despite any bad wrap from the uninformed masses and well meaning dietitians, is a complete blessing for people like me who have defective mitochondria and inappropriate energy storage/partitioning. Ie: I can't eat like my body handles sugars well, because it doesn't. Working with that instead of fighting against it has made maintenance far easier AND more pleasurable
There's loads more, but that's the basics.