I have a pair of trainers that I wear day-in, day-out. They are my workhorse trainers and they didn't cost much to buy, in fact I think they were around £15 so I don't expect much in the way of comfort or durability but they are generally great, especially for the price.
Today I discovered a flaw. They have a small loop on the back, like many other trainers and shoes do, which helps you pull them on. It's like an in-built shoe horn. It's a little bit of material sewn on the back in a kind of loop shape which you put your finger through and use it to pull on your shoe. Except my finger doesn't fit in it. So it doesn't work, for me. Now I have quite small hands for a guy, and these are men's trainers. I also, being a climber, have stronger than average fingers and even just putting the very tip of my finger in it doesn't work. So my point is, if I can't get my finger inside it and pull on the trainer using this nice little loop, then I'd imagine that not many other guys can either. So it's pretty redundant.
In terms of this particular pair of trainers it would be a better design choice to either leave the loop off – as it adds extra manufacturing cost, weight and materials for no extra benefit to the end user – or make it just a little bit larger. So the designer either didn't really user test or didn't really think properly about who would be using that particular little loop.
What can we learn from this? Well it's the same for every piece of design; be it communication design, a website user interface, a pair of trainers, or a house. If there is one tiny little bit of that piece of your design that doesn't work for your intended user then you have failed as a designer to address their needs. If it doesn't serve a purpose then it shouldn't be there at all, if it serves a purpose but doesn't quite work, then keep improving it until it does work.
I quite like my trainers but that little loop is a bit of an annoyance and if it meant paying a little extra to have a working loop, then I'd probably go for it. It's not something that I would have noticed when trying them on, I have only noticed it through use and that's the scary part, especially if you run a website for your business because chances are that you don't actually use your own website so you will not notice its flaws and little annoyances, but your users will and it might just be enough to make them go elsewhere.
Before releasing your product or service to the end user, make sure that you user test and, more importantly, user test both as yourself and as your intended market.