You can't understand it. Your heel is slipping out of the back of your shoe, and your little toe is aching again. Once again, your shoes don't fit!

Excuse the pun, but there seems to be a conspiracy afoot. You can't find comfortable footwear to save your life.

If it's any comfort, you're not alone. The culprit is usually a common problem with the way shoes are made and purchased.

You see, most people buy shoes by length. Whether it's a women's size 10 in America, a 42 in Europe, an 8.5 in England or a 28 in Japan, it's the length that determines the size.

But what of the width?

We have a dozen or more choices for length, but, with most brands and styles, we're lucky if we have three choices for width: narrow, medium and wide.

And here's the secret you've read this article to discover: it's the width that determines the comfort of your footwear.

What if they offer only three choices, and you need the fourth?

The very best shoe brands offer eight or more widths, from AAA (very narrow) to E (very wide). But most manufacturers can't afford to make and stock so many choices. They go along with our ignorance of proper fit so we'll continue to settle for what they have to offer!

Think of the importance of shoe width this way: when you choose the right width, the shoe caresses your foot along the sides and across the top.

Here's the shoe fit key, in an nutshell: fit the size by making sure the widest part of your foot lands at the widest part of the shoe, giving your toes some wiggle room. Then choose a width that holds your heel and instep snug in place.

And here's a bonus tip, at no extra charge. Most shoes are fit too short and too wide. When the width is right, you may need to go to a bit longer size.

If you have to pay more to find brands and styles that come in the widths you need, treat yourself. The shoes will pay for themselves on your feet instead of kicking around idly in your closet.