The question arises not on how the shoe looks but in terms of its performance. For example, the rubber sole begins to wear off, is that just an initial wear or is it a sign that the shoe must be changed? In practical terms some people wear the shoe until a hole comes about. But, in terms of performance when is it time to change it in order to have a well balanced shoe that prevents one from developing an injury such as ankle twist, improper aligment, etc.??