How do you teach a 3 year old about disappointment?

I had to see, for the first time tonight, my three year be let down by a complete stranger. I responded to an add on Craigslist for a Little Tykes picnic table. It would have been perfect for the boys in the backyard. I was the first to respond and spoke to them on the phone. I told them we were on our way. The man asked that I call when I got close so that he was expecting us. I called him just 20 minutes later once we were closer and almost to his house. He informed me that he had just sold it to a lady that was at his house buying another item. He apologized and we hung up. I had already shown Carter a picture of the table and he was super excited! As we were turning around to go home, I told Carter that we weren't getting the table and were going home. He started to tear up and was so disappointed. How do you explain to a three year old that sometimes we run into not so nice people? In the midst of him crying he told me that he was sorry that we didn't get the table. My heart just broke. I explained to him that it wasn't his fault by any means and sometimes people just aren't very nice. I know this is the first of many times that he will be let down in his life but three years old just seems so young to start those "life" lessons.