Why are we grouping bits into bytes (8 bits)?

Another ‘magical truth’ I saw a lot is that someone decided – all of a sudden – to use 8 bits to cook a bigger unit, the byte. And that he could have used any other amount of bytes…

But again, another value we were eager to represent with bits is text.
And in order to do this, we need at least to code our 52 characters (26 in lower case and 26 in upper case), the 10 digits, the space character, some punctuation, etc.

We end up with the need to use 7 bits, the American Standard Code for Information Interchange (ASCII) that was introduced as teleprinter code in 1963 by AT&T. And we then needed an extra bit for parity (error encoding).

Then we were using 8 bits to encode each character… which was later known as a byte.

They were nothing arbitrary about its design. Just pure logical needs.