Simply playing a guitar at gigging volume (even finger-picking) will put it out of tune - no matter how well-made it is. Using or moving a capy will do so too, and if you change the pitch of just one string the neck will twist slightly and put the others out. Then there's changes in termperature and humidity. Plus you can only tune a guitar accurately to one chord. As soon as you finger another chort it will be slightly out. Tuning is always a compromise, so sometimes just needing to play in first position, standard, in a different key, will require a slight ajustment.

You simply HAVE to tune on stage, all the time. People should be educated to understand that.

An out of tune instrument - even if ever so slightly out - simply does not work. It won't ring properly.

You'll never get a chance find out how long you guitar will stay in tune on its own if you're using it properly.