A photo of backache relief medicine has been circulating on social media recently. Seeing it inspires a “duh!” moment: If you have a backache, it’s going to be hard to bend over and pick up the medicine from the bottom shelf—and never mind getting close enough to read the offer on the tag.

So…why did this happen?

Odds are that the back relief subcategory within the pain relief category doesn’t sell as well some other subcategories, such as general purpose pain relievers. The better-selling products get preferential placement, at eye level. But that rote decision ignores the fact that the users of backache relief medicine really need the product to be shelved a bit higher off the floor.

Paco Underhill, founder of Envirosell and author of some excellent books about consumer psychology, tells a story in his book Why We Buy that highlights how important shelf placement is:

Another such “accident” of patient observation and analysis happened during a supermarket study we performed for a dog food manufacturer. When we staked out the pet aisle, we noticed that while adults bought the dog food, the dog treats—liver-flavored biscuits and such—were often being picked out by children or senior citizens. We realized that for the elderly, pets are like children, creatures to be spoiled. And while feeding Fido may not be any child’s favorite chore, filling him up with doggie cookies can be loads of fun. Parents indulged their little ones’ pleas for treats here just as they did over in the cookie aisle.

Because no one had ever noticed who exactly was buying (or lobbying for the purchase of) pet treats, they were typically stocked near the top of the supermarket shelves. As a result, our cameras caught children climbing the shelving to reach the treats. We witnessed one elderly woman using a box of aluminum foil to knock down her brand of dog biscuits. Move the treats to where kids and little old ladies can reach them, we advised the client. The client did so, and sales went up overnight.

Similarly, Underhill writes, cosmetics, clothing, and drugs for older and heavier customers aren’t perceived as glamorous and therefore receive less-than-prime shelf real estate, usually on low or high shelves. This attempt by store managers to raise the visibility of “sexier” items makes it hard for shoppers to physically retrieve those products intended for them—which leads to poorer sales, perpetuating a cycle of permanent exile in a poor location.

Considering the buying power of aging Boomers and the growing waistlines of American shoppers, this is a bad strategy.

When planning where to shelve an item, consider the following five points.

1. Who is your consumer? Will they need your product to be shelved in a particular place to see or reach it?
Cereal and snacks targeted toward children are common examples: These products are often on low shelves, the better to see them and influence parents to buy them.

2. Is there a special need? Will visibility in a certain place help?
Many stores have portable racks with umbrellas that they move to the front of the store when it is raining—especially stores where many shoppers arrive on foot or via public transportation. This placement gives shoppers an immediate solution for a problem they might have: being wet.

3. How big is the product?
I worked on a new product that was just a little taller than most of the products in its category. The manufacturer wanted it to be shelved with comparable items, but it was taller by just enough that it didn’t fit on the shelf. The top shelf was the only place where it would fit, which is not what the manufacturer wanted. Size is an important consideration when developing packaging.

4. Do you want consumers to compare your product with others?
I worked with a well-known snack brand, and one of their leading products was shelved with cookies and crackers. Our research found, though, that shoppers commonly substituted this product with chips and pretzels. By not being shelved with those items, the product wasn’t part of the consideration set for undecided shoppers. Another brand I worked with had a low-price offering and always wanted it to be shelved next to store-brand items so that shoppers could easily compare prices.

5. How will it be placed in a shopping cart?
One Northeast retailer always placed its large bundles of paper towels on the bottom shelf, a common enough location for large and heavy items. They had a goal of trading shoppers up to larger sizes (with the related higher prices), and they found that moving the large bundles to higher shelves increased sales because they were more visible. They had feared that shoppers would struggle to maneuver the bundles, but given the light weight, the higher placement turned out to not be a problem. Large, heavy bags of dog food and cat litter didn’t receive the same treatment.

These questions are just a start, and they will help you do your homework before you ask for specific shelving locations. Remember that if your shelf placement varies among retailers, you should analyze the unit movement for each placement to see what works best. This analysis will give you the best evidence that one placement works better than another.