In case you are wondering, that is not a leg or an arm - it's part of a chair in the reading room LOL.
There are a lot of times we miss things. We walk past something interesting of that is worthy of our attention. Even the best photographer in the world has done this.
For the most part when I take a photo it's something people will look at and not know it's there. Something that they miss altogether. I have noticed that personally I tend to like the photos of people who take photos of every day things or people. The shots make things stand out that we don't see as we are over exposed to them.
I follow a few photographers on the net on several sites and enjoy their work for just this reason. They see things that we miss. The best thing is, if your average person goes out looking to do just this - they will often fail.
I can't tell you what attracts me to the things I take photos of, all I know is if I go looking for it I will not see it. It just has to kind of happen and out comes the phone or the camera and I take the shot.
Sometimes I play with the image after to make it not as it was when I took the shot, but most of the time it's just as it was when I saw it.
One fellow I follow "Felix" takes a lot of shots of people. It's a common thing you are part of and don't see in the way he sees it. When you look at the photos they stand out and you understand what he is trying to say. A lot of them are that "alone in a crowd" kind of thing. Others are just a slice of life that we pay no attention to.
This is how we think though. When we see it, we don't notice it. When it's pointed out, we can't miss it. After all, how many times has someone been walking or driving along and the sun is setting - only to notice it when someone says "look at that"? It happens all the time. Our brain does not need much distraction for us to miss what is right in front of us.
Try some day soon to clear your mind and just look around. Don't force it, just let it happen. See if you don't realize that there are a lot of things of interest and beauty that you walk past every day. Just sit on a bench some place or in a coffee shop and look at people. See what you have not seen in the things you see all the time.
Once you see the world in this different light, it is hard to go back to the blind doldrum of every day life. Unfortunately most people are either unwilling to or unable to see the world as it can be and not as they think it is.