The movement of the finger while playing left hand pizzicato is different to normal finger action, since the pizzicato movement pulls into the palm of the hand while the finger action is a lift and drop from the base knuckle.
Left-hand pizzicato often appears in virtuoso repertoire, but is also useful in the early stages of playing to develop independent finger action.
If you are using two fingers (one to produce a note and one to pluck), the finger stopping the string needs to have firm enough pressure.
When developing left-hand pizzicato as a virtuoso technique be careful not to push your body to learn too much too soon. Take breaks in your practice and if you ever feel discomfort, it is a good time to rest your hand!...