All is right with the world. The farthest thought from your mind is that inescapable day, several hundred miles from now, when these seemingly immortal shoes will die. It's a slow but steady process, as each delightful stride chips away a bit of shoe integrity. Even if you save them exclusively for running, your treasured shoes will eventually break down and die a slow, miserable, wretched death. The outsole will grow smooth and shallow, the midsole will wrinkle and deform, and those soft synthetic suede stabilizer straps will stiffen and crack.
Dead shoes look very much the part.
But if the appearance of the shoes doesn't provide enough clues, your body may be the first harbinger of shoe death. Speed work and longer runs will require more recovery, or the first few steps out of bed each day will be a limping dance of sharp pain. Ultimately those final miles will be filled with screaming protests from every tendon, ligament, and muscle located south of your singlet. Attempt bypass surgery with a pair of new insoles. They're soft, they have a big arch support, and they slip right in to replace that gnarly piece of foam that, after 600 sweaty miles, breeds an unimaginable assortment of aggressive foot cooties.