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Quite apart from the difficulties of accurate miniaturisation. there were other reasons why pre-digital watches were unreliable.
The hands of a watch were kept moving by a spring inside the watch which gradually unwound. This spring had to be wound up with a winder, which was a knob on the side of the watch. Watches had to be wound up either daily or weekly and it was all too easy to forget. Hence they went slow or stopped.
Interestingly the winder was only 'wound' when it was setting the positions of the hands. In all the watches I knew, it was rubbed backwards and forwards with a finger. So there must have been some system whereby either the backwards or the forwards rub did not contribute to winding the spring.
The mechanisms for watches were susceptible to dust which made them work erratically. I never understood how the dust got in as the back case remained tightly closed. Nevertheless when a watch became unreliable, it was sent for cleaning, even though the result was not always satisfactory. The mechanism seemed to have got irreversibly damaged.
The winder, pulled out slightly, moved the hands as well as winding the watch. So it was in frequent use which often caused it to drop off and be lost. A jeweller who doubled as a watch-mender could normally provide a replacement, but of course at a cost and not necessarily matching.