Why do chains break? Broke the rivet out of a SRAM 9 speed chain last night whilst trying to climb something steep. I'm not worried about it - the chain's had a good (if muddy) life. I'm just interested in the mode of failure and if there's anything I can do to reduce the risk next time.
keep it clean and lubed, avoid crosschaining
normally the pin twists out of the fishplate from what I can see. I've not broken one in a while that wasn't due to chainsuck twisting a link (that was a fun evening). I'd say that allowing the chain to stay dirty probably leads to wear at the pins and fishplates and eventually something gives. I take my chain off the bike to clean it in an old waterbottle with degreaser (tried petrol for a while, which worked OK but was 'orrible). Soak and shake whilst working on the rest of the bike. Test the cleanliness of the chain by grabbing a length and twisting it along its length. You will feel the grit between the plates if there's any there. clean again if needed.
Dont put exccessive pressure on the chain whilst changing gear, change gear for climbs etc early.
Keep it clean and lubed as said above.