I lose something all the time
Perhaps, you just have the holes in your pockets... Or you are disorganized. However, even the very smart and routine type of people turns to be very forgetful. For example, you used to put your wallet and keys in the same place all the time. Once it seems to you that you put them there again as usual, but it turns out that you did not. Usually you are so busy with your everyday life, work and family matters, so, you are not able to remember everything and keep everything under your control. So, try not to keep so many thoughts in your head, do not make long-termed plans if you are not able to keep them in your mind and get the things organized. Try to focus on the single thing at the same time. As you see, the order begins with your personal thoughts organization.
Careless is another reason for your bad habit. If you do not mind to lose something all the time, it is ok and you can leave everything as it is. But if you do not feel comfortable to ask your neighbor's child to open the door of your house from inside, it is high time to learn how to focus your attention. The simplest tests are proposed for the small kids. You are showed two pictures; the second one is a little bit different from the first one. Try to find the difference. Or write down the things which you forget regularly. Visually, you can understand when you have to be more attentive.
Some psychologists suggest an idea that a person who loses something regularly, just tries to avoid some events. For example, if you lose your house key, you do not wish to return home. That is why your subconsciousness prompts the way out – just to lose your key.