In my case it was my parents at a very young age. When you're a toddler, you basically eat what your parents give you. You're reliant on them as you can't make your own decisions, can't do your own shopping, etc. An overweight 5 year old is the fault of the parent. Yes, I'm sure young children "want" a chocolate bar, bag of crisps, biscuit, etc., but the parent has to facilitate that and can, if they want, provide alternatives.
I was clearly overweight in my toddler photos. By the age of 7, my school reported me to social services and my me and my mother were called in to see the "school doctor" at the local SS offices. I was put on a strict diet and had to return every week for a weigh in. At home, my mother massively over-reacted and every meal became a salad. Parents and brother continued to eat fattening crap, like going out for fish & chips at supper time every night, sugary cereals for breakfast, etc etc., whilst I sat watching nursing my lettuce leaves.
Unsurprisingly, I rebelled and started taking crisps, biscuits, etc from the cupboard whilst they weren't around. Ended up eating more than I would have done normally, just to spite them, so my weight kept going up rather than down! (Remember I was only a 7 year old). Inevitably, I was found out, and the snacks etc were locked away. So I started stealing my Mum's milk money to buy crisps at the school tuck shop. This was quickly reported back to the school doctor, so I was barred from the tuck shop. At home, parents and sibling still happily eating all the crap they could find whilst I had salads! So, I started giving money to friends to buy crisps for me from the school tuck shop and would eat them in the toilets at breaks and lunchtime. Not just the odd packet, it became an obsession and I was almost getting to the stage of seeing how many packets I could stuff in at a break time! Weight still increasing, but parents/doctor couldn't work out why, and (I can't remember exactly when or why) but the weekly weigh ins just stopped when I was probably 8 or 9.
Unfortunately, the behaviour/habit had been established and I was well and truly a closet binge eater by the time I was 10. Then parents bought a convenience corner shop that we lived above. Literally surrounded by sweets, chocolates, crisps, biscuits, ice cream, etc etc. I never stood a chance. I'd just constantly steal stuff from the shop or the store cupboards (which were in the back room, hallway, landing etc so easily accessible). I ballooned to 20 stones by the time I was 16! Parents seemed to have given up completely by then so I was also eating normal "crap" with my family at mealtimes.
The binge eating behind closed doors continued throughout my adult life, even in marriage. At home, I'd eat normally, healthily, etc., my OH is slim and healthy. On the drive to work, however, I'd stop off at a garage to buy a pie or two, couple of bags of crisps, couple of chocolate bars, etc to eat on the way, same on the way home! It was always a joke at home that I'd lose weight on holiday despite eating more (and the wrong foods) than when I'd be at home (of course it was because I wasn't stuffing myself on the drive to/from work!).
When I tipped the scales at 25 stone, I knew I had to do something drastic to change my behaviour. So I gave up my job and got a job much closer to home, shorter commute, so I couldn't binge eat on the way there and back. After a couple of years, I'd lost 5 stone, OH couldn't work it out because I was eating the same at home as I'd always eaten. (I'd still binge eat given the opportunity, say if I had to drive to see a customer or for a course etc., I'd be back in my old ways of stuffing myself in the car).
Now I'm down to 15 stone. I'll still binge eat occasionally - i.e. if I buy a multipack of crisps or Mars bars, etc I'll eat them all in one go despite promising myself "only one". To counter that, I try not to go shopping on my own.
Behaviour/Habit is a massive part for me. I don't think I'll ever be able to stop binge eating, so instead, I try to organise myself so I don't have the opportunity to buy it. I try to go shopping with DS or OH. I try to avoid long drives on my own.