Things that are very well put

From this guitar site (the first paragraph is the timeless part – the second is there for context)

If you think theory is boring, think again. Think of it, not as something you have to know in order to do something right (as most schools teach grammar, e.g.), but as a way of explaining what it is that you already know.

All chords belong together in families — the famous three chords, plus relatives and friends. Every song, at least in the popular music repertory, has a keynote (also called the ‘tonic’, hence abbreviated T), the main tone or chord around which the song revolves. This is almost always the tone/chord on which the song ends, and most frequently the tone/chord on which it begins, but that is not always the case. It is safest to go by the end.  A song in C major ends on a C major chord, etc. The keynote represents the stable level from which everything develops and to which it all returns.