I won't pretend I understand even the basics of QFT, but from what I've heard about electrons, there are really two main ways of thinking about them. Quantum Mechanics describes an electron by a wave function who's squared magnitude gives the probability of finding the electron in a certain position or with a certain momentum. QFT, from what I understand, describes the electron as an excitation of the electron field. Both of these models describe the electron as some excitation of a mathematical field permeating space and time. My question is this:
If an electron really is described in this way (either using a wave function, or a field), what properties of the field, or of space-time itself, make it so the electron is stable (i.e. the excitation does not spontaneously decay, stop existing, or change) what causes the electron to continuously remain the same from one moment to the next)?