I'm currently in the process of doing "boot camp", and needed to get new shoes. One of my instructors said you could expect to replace your shoes every 200 or so miles, so every 2 months or so for you if you run 3 miles a day.
Fools ignore complexity. Pragmatists suffer it. Some can avoid it. Geniuses remove it. -- Perlis's Programming Proverb #58, SIGPLAN Notices, Sept. 1982