If you are getting blisters from wearing them, you need to stop wearing them. Blisters can become infected and cause you more problems than you care to deal with.
As harryvan stated, poorly fitting shoes will affect your posture, walking and outlook on life.
Improper fitting shoes cause stress on the back, are the cause of many foot problems such as bunions, corns, torn flexor plates, hammer toe and a few more problems not to mention that they make you feel miserable which in turns makes every one around you miserable.
So in short it is your fault that we are all having a bad day.
Get some new shoes and have a healthy, happy life.
Good luck and best wishes.