I guess I’m in the same boat as the OP. I have broken many chains. First Shimano chains years ago, then SRAM more recently.
I’ve learned a pulse technique to shift on surprise hills. Ram the hell out of the pedals for a quick boost, then back off and shift a few cogs as you follow the momentum with the crank. But of course if a chain is about to break it will always be more likely to do it under load, under shifting, and when crossed.
Are your chains too long? If the chain tension is very low as you drop to the small front ring the chain can ride up on the tips of the teeth, causing jumping and breaking. This can be exaggerated if you are in the big chain ring and small cassette side and choose to shift the front der first. Small + small = loose chain.
Are your chains too short? Most people check for a little remaining action at the rear der when sizing a chain, but that isn’t the whole story. The chain has to have enough length to jump over teeth too. This is exacerbated if you are in the big chain ring and small cassette and choose to shift the rear first. Cross chain plus climbing onto the teeth needs a little extra. Mostly this isn’t a problem since you have to size by two links at a time, but it should be checked.
Are your old chains worn out? This causes all sorts of weird dynamic loading things to happen and increases the odds of failure. There are tools, but an easy way is to compare 10 or more links of a new chain with a used one. When the size difference is noticeable, it is time. Since these things aren’t really sealed, you might just be wearing out chains faster than you think.
Does your chain suck? If you suck the chain into the small ring and BB gap it often gets yanked in through a gap that it doesn’t really fit through. I’ve found pretty significant side link plate damage after a sucking event. Of course if my chain failed later, I would blame all the damage on the breaking event. I wouldn’t consider that the gouge in the link was from earlier. I’ve found the part that is actually stuck may be a handful of links from the part that was mashed through the gap because I force the pedals before I realize I’ve chain sucked. Let the jokes begin.
I've always had SRAM mid to upper grade chains and always brake them sooner or later. I put one of the higher up KMC chains (the gold one, I forget the model) on my Moonlander and that thing has been dang durable for how much crap it has been covered in.
