The great teacher Frederick M. Noad once wrote in his book (Solo Guitar Playing Vol. 1): “technique seldom stands still – it either advances or retreats.” This is true also for pieces of music. We guitarists work hard to memorize and polish each piece, but if we don’t establish good practice habits to ensure that we return regularly to each piece we learn, our hard work will certainly erode. Even allowing so much as a two week lapse can be enough for a player to lose the ability to play a piece fluently.
The good news is that this gradual rustiness with any given piece is easily corrected after a brief review of the sheet music. But because performance opportunities can often present themselves unexpectedly, experienced musicians know the tremendous value of creating and meticulously maintaining their own personal REPERTOIRE. Over the years I have observed that a good musician performs what is in their repertoire, and seldom engages in ‘attempts’ to play things outside their repertoire. Good musicians judge accurately what they know and what they don’t know before attempting to play in front of an audience.
One piece of music played though with expression and confidence makes a better impression on an audience than 100 stop-and-go fragments, played with lots of mistakes.
What I have also observed over the years is many guitarists struggling to maintain performance abilities without a firm concept of repertoire. The French origin of the word “repertoire” makes it seem refined, but the concept can manifest itself as a short list of titles. Rock music has a term for the same thing: “set list”.
It doesn’t matter if you are a day-one beginner or an advanced player. You should have a page in a notebook where it is written down a list of musical selections you know how to play beginning to end, from memory. You should look at this list and play several songs from it daily. That’s all you have to do to keep all your songs sharp and ready to be performed at a moment’s notice.