Strange pair of shoes

Sales have started and many people decide to go shopping, to find some bargains.
Last year, I showed to my brothera pair of shoes that I had seen, and I was sure he would like them. We come into the shop to buy them, but they didn't have his size.

The other day, he phoned me (he lives in Lleida), and he asked about the same shoes we had been seeing the year before. “Try to buy me the shoes, please. I really like them.”, he toll me. Two days later, I went to the shoe shop. The size which my brother needs it was in another shop, but they offered to me to bring them, and I could pick them up the day after.

I came back to the shoe shop, just to pick the shoes up. Many people were into, trying to find bargains. I paid and I got out.

This Saturday, his wife was in Barcelona and she picked the shoes up. When she arrived at home, my brother tried them on and he phoned me saying the shoes were O.K.

On the next Monday afternoon, when I arrived at home, there was one phone call from my brother in my phone, and in my mobile also. I phoned him to ask what happened. The pair of shoes was wrong: one shoe was in his correct size, (it was the one he tried on), but the other was one size and half more than the other. In the first time, he thought his feet were different, but finally, he compared the two shoes and he cheked the difference.

This is a long way for a new pair of shoes. But, the most surprisingly was the shop assistanct's answer when I phoned to the shop, to explain the situation. She said: Many people buy shoes in a different size because their feet are different. If you want a solution, try to find your complement. Since that moment, my brother is looking for it. But, what complement?