It took me such a long time to realise the worth of decent trainers. I couldn't understand for the longest time why I kept getting shin splints after I ran. Turned out it was the lack of proper heel support.
My shins work as a barometer for when my shoes are at the end of their life.
I go by the motto "always look after your feet" when buying shoes, it's amazing the difference it can make and yet is overlooked by so many people.
Kept banging on about it to Mrs M after a succession of cheap trainers and aching feet (her arches collapse, you can spot it a mile off), she finally let me buy her a pair of Merrell's for walking and within about 5 minutes she realised the benefits of a decent pair of shoes.