E.g.:
> In some sense I put in many of the programming features kicking and screaming [...] Every system I looked at had its own universal Turing machine built into it somehow, and everybody’s was a little different from everybody else’s. So I thought, “Well, I’m not going to design a programming language; I wanted to have just a typesetting language.” Little by little, I needed more features and so the programming constructs grew.[...] as a programmer, I was tired of having to learn ten different almost-the-same programming languages for every system I looked at; I was going to try to avoid that.
etc. (https://www.ntg.nl/maps/16/15.pdf)
and:
> I was really thinking of TeX as something that the more programming it had in it, the less it was doing its real mission of typesetting. When I put in the calculation of prime numbers into the TeX manual I was not thinking of this as the way to use TeX. I was thinking, "Oh, by the way, look at this: dogs can stand on their hind legs and TeX can calculate prime numbers."
(Coders at Work interview)
In fact, if you use TeX the way Knuth intended and uses it, then the use of macros or programming is really quite minimal. It's only LaTeX that to pursue a better document interface for the user, ends up writing horrifically complex macros -- Mittelbach mentions that nine out of ten "dirty tricks" mentioned by Knuth in the TeXbook are actually used in the source code of LaTeX!