Shifting too much.
There's a Shimano design that has a habit of breaking in the shifter leaving an annoying to remove stub, I think it was the 6800 and their 105 equivalents.
It’s because people pull the dual brifter lever inward while changing gears, eventually shredding enough wires to make the cable snap and leave the cable head firmly lodged in the newly stuck ratchet.
Shifting too much.
There's a Shimano design that has a habit of breaking in the shifter leaving an annoying to remove stub, I think it was the 6800 and their 105 equivalents.