The fit of a shoe is all about perception, not necessarily reality.
From the time we are kids, we grow into our shoes and get used to the feeling of what a shoe should feel like on our feet. As we grow however, we grow into our shoes, and get used to the feeling of snugness. That feeling then becomes the new normal, and what we tend to seek when trying on shoes. Just because you have been a certain size for most of your life, doesn’t mean you still are the same size. We get used to things pretty easily, including shoes that are sometimes two sizes too small!
Imagine having to type or write a report while your hand is being squeezed. How quickly do you think the cramping and difficulty will begin? When you wear shoes that are too small, it’s precisely what’s happening with your feet. True, the foot lacks the need for dexterity and can be a lot more utilitarian than the hand, but the premise is the same; if a body part has a job to do, why not let it do it’s job in as unrestricted manner as possible?
The feeling or sensation in our feet is also usually the first to go; therefore you should NEVER just rely on how something feels. A good test is to remove the sock liner of the shoe and stand on it. Make sure that the foot fits within the confines of the liner. If it does fit, then you can rely on the fact that the shoe is properly sized. If the shoe you’ve been wearing happens to have been too small, then realize a properly fitting shoe will feel too big. It can take several weeks to change perceptions, and have it seem as though you are not walking out of the shoe. But proper fit is the most important part of shoe buying.