speech is made of bits and pieces of things you’ve said before. We have the opportunity to optimize
much of our speech as we practice words, tones, and tone combinations. Note especially that there are very few
tone combinations in Mandarin (64 tri-tones), so it’s quite possible to
practice all the combinations in a short time, and it’s reasonable to assume
that they get practiced every day.
Thus, they could easily be perfected, matching whatever criteria the
speaker wishes to optimize.