Say, there is a word that used to be pronounced [ten] but gradually shifted to [tin]. I get it. There is always variety in how people pronounce words. Throw in some population dynamics, and the median of this variety gradually shifts over generations, the difference accumulates - and voila, a new sound.
What I just can't get is how could the same change affect not only [ten], but every other word with the [e] sound too? Even in drastically different phonetic environments (not just in, say, words that rhyme with [ten]).
How exactly does it happen, and why? Does it happen to most words simultaneously, or do some word(s) shift first and the rest follow? If the latter, what makes them follow instead of just retaining a different vowel?
Is there some psychological mechanism, or perhaps some kind of population dynamic, that ensures the regularity of sound shifts?