This happened all the time. My mind thinks a lot. Often time, I was not aware of thinking while I was on an activity.
Take the example of driving a car alone to a destination. Driving is almost auto-pilot and I arrived at a destination with so much thoughts in between. Thoughts can be planning thoughts, thoughts of the past, angry thoughts, revenge thoughts, worry thoughts, running commentaries in the head, etc. Not once, I was fully present with just driving the car and knowing the exact conditions on the road.
I can give more examples. Taking a shower always resulted in time to think about many other things but not with just bathing/showering. Eating a meal, ironing clothes, washing dishes, and waiting in a queue are other examples.
Mind wanders and I lack attention to details of activities I am at. That is the nature of minds and we shouldn’t blame ourselves for thinking. Let it be but the least we can do is to be aware that thinking had taken place. It is also good practice to be fully with the activity. That is concentration practice. Just to illustrate, when I am reading a good novel, I can be fully immersed in the story and my mind did not run around. We can try this out with other activities, enjoying the activity on hand.
When mind concentration is good, the mind is sharp. One can enjoy the activity better. For example while walking in a park, one can pick up subtle fragrance of flowers, beautiful sounds from birds and insects, and beautiful sights at the park. One is then fully immersed in the activity. Enjoy the moment of just walking in the park!