I think the chain slipping off the cogs is one of the most concerning failure modes because it tends to happen only under heavy acceleration, e.g. to dodge traf

I think the chain slipping off the cogs is one of the most concerning failure modes because it tends to happen only under heavy acceleration, e.g. to dodge traffic at a busy intersection. Everything can seem fine and then you're stranded without power exactly where you need it most. It's worth regularly checking for wear and correct adjustment.