A Wandering Mind is on the look out for trouble or danger. It is like a guard dog. It is not relaxed. A Focused Mind is just looking at what is happening in front of you and can enjoy itself. Research suggests that a focused mind is more content and happy. So if you are doing something with your full attention you are more likely to be calm and not worried about the past or the future since neither exists in the present. If you have a problem it is unlikely to be happening in the present. Typically it is about what has happened in the past and is coloured with regret. It may also be about something that hasn’t happened yet ( and may never happen ).You can make yourself very anxious thinking about ‘what ifs’. Imagine speaking to an audience and thinking ‘I hope they like me’. Better to focus on what you are saying.
I am not saying that day dreaming is unhelpful. It can be enjoyable if done on purpose. I am saying that your thoughts will control you and your mood if left to wander and ruminate.
So, try and catch your mind wandering and come back to what is in focus.It could be your breathing. It gets easier with practice. If you are reading and drift off, simply come back to where you left off and read again with full attention.
Practice makes permanent.