Nothing can ruin a hike or a backpacking trip like a pair of ill-fitting hiking boots.

It's a universal truth that cannot be argued.

"No matter how beautiful an area you're in, if your feet hurt, you're going to be miserable," said Fresno outdoorsman Scott Shively.

"People ask me all the time, 'What's the best boot on the wall?' My answer is always: The best boot is the one that fits your foot the best."

Even though boots are the most essential piece of backpacking or hiking equipment, few people actually take the time to ensure a proper fit. Believe me, I know.

For years, my shoe size was 10½. I assumed it would never change. In my mid-20s, though, backpacking started becoming less and less

pleasurable. Each time out, I'd come home with quarter-size blisters covering each foot. Instead of mileage, I started measuring distances by the number of times I had to stop and replace moleskin.

This pattern might have gone on forever (or I might have stopped backpacking completely) if not for a man named John Taylor, the now-retired owner of Taylor's Family Shoes in Bishop.

Before allowing me to make a purchase, Taylor insisted (over my mild objections) on measuring my feet. When he said I was a size 12, you could have bowled me over with a feather.

Needless to say, I've worn size 12 since. And blisters are a thing of the past.

For years, I assumed I was the only person stupid enough to insist on wearing shoes that were 1½ sizes too small. Turns out I'm not.

"It's really common," said Dr. Kathryne Rupley of the All Valley Podiatric Group in Fresno. "People are in denial about their shoe size. I don't know what it is -- it's just a number -- but both men and women don't want to admit their feet are getting bigger."

Rupley explained that as people get older and heavier, the increased pressure (i.e. weight) causes their arches to collapse while ligaments become permanently stretched. So not only do feet grow larger, they also grow wider.

Carlos Salazar, a sales specialist at REI in Fresno, said getting the correct fit is the most important element of purchasing hiking boots. Function ranks second, with aesthetics a distant third.

To ensure a boot fits properly, Salazar recommends people try on at least four or five pairs in the store. If the boots are meant for backpacking, he'll weigh down the customer with a 35-pound pack.

"Even if the first boot fits great, I'll have them try on something else so they can compare the original fit," Salazar said.

How do you know when your boots fit properly? As you first put them on, slide your feet as far forward as possible. If you can slide one finger (but not two) between your heel and the back of the boot, you probably have the right length.

Now take a few steps. There should be very little up-and-down movement in the heel, and your toes should not slam into the front of the boot when walking downhill.

"It's not going to fit the same as a regular shoe, but a well-fitting boot should feel pretty similar," said Shively, camping manager at Herb Bauer Sporting Goods in Fresno. "They shouldn't feel like downhill ski boots."

There are other factors to consider as well.

When one of her patients seeks advice on hiking boots, Rupley suggests they always try them on while wearing the same socks they intend to hike in. She also recommends shopping in the afternoon.

"Everyone's feet are a little larger in the afternoon than they are in the morning," Rupley said. "They're more swollen and spread out from walking."

In recent years, hiking boots (along with packs, tents and sleeping bags) have been swept up by a trend that some in the industry have termed "the ultralight revolution."

This means that manufacturers, thanks to advances in technology, are making boots from lighter-weight materials, often sacrificing durability to shave a few ounces.

"The great balancing act is to go as light as you can and still maintain the stability that you need," Shively said.

Even though new, lightweight boots might feel great in the store, they still require a break-in period of at least 25 hours before setting out on a multi-day trek.

Take it from me. Nothing can ruin a good hike more than the agony of the feet.