Hold a pencil in your hand, look at your watch to measure the time, and try to focus your full attention on the pencil. Look at it from all sides, trying to imprint its image on your mind.
The moment you discover that you lost your focus, look at your watch to measure the time.
How long can you focus on the pencil, before your attention or your eyes wander somewhere else? Can you measure the time in minutes, or just in a few seconds?
If you can measure the time in minutes, you are lucky, but if it is only seconds, you need to do something about your focus.
When you write a letter, read a book, or study for an examination, how many times do you stop, and either, think about unrelated subjects, or get up and do something else?
When learning a new skill, working, or doing anything else, do you focus on what you are doing, or does your mind wander to other things?
Are you absent minded in situations that require complete focus of mind?