Adopt a Run
Based on arch type, cushioning level, and pronation style shoe need to be fit or "matched" properly to specific feet. Shoes have a finite life expectancy whether used or unused. Under normal circumstances this means switching shoes every 300-500 miles or about 6 months of consistent wear. If you work, laugh, play, and also run in shoes, this timeframe can be very different.
I.e. Standing on your feet for 4 hours a day without any running = 6 month replacement time