A friend of ours has left a mandolin with us, just for a visit. It's a very nice mandolin but he hasn't been playing it much, so he wanted me to "play it in" and bring it back to sounding its best. I play it most of the time for my daily practice, and its sound is indeed improving. This is something that happens with most instruments. If you play them regularly, they sound better than if you don't.
Some folks don't believe this happens, and say there's no such thing as an instrument's sound improving from being played. But I believe that they ought to say, "I haven't heard this happen myself." Maybe they've never heard an instrument improve, but it sure happens, and folks all over the stringed instrument world are aware of it.
It's well known in the violin world that instruments sound better if they're played. A friend of ours was in a group which played a concert in Cremona, Italy, where many of the old master violins were made, long ago. He and his friends visited a violin museum there. Among all the beautiful old violins there was a little old man whose job it was to play them, each of them, every day, in order to keep them sounding their best. What a job, to play millions of dollars worth of violins every day of the week. Life is hard! But it did keep the instruments sounding great.
So why am I telling you all this? Because it applies to the instrument you play, whether it's a mandolin, fiddle, guitar, or banjo. Play it every day, and keep it sounding good. You'll have your own million-dollar sound.