I've experienced this many times. I've been walking to and from work most days for the past several years, about 30 minutes each way. In the morning I listen to

I've experienced this many times. I've been walking to and from work most days for the past several years, about 30 minutes each way. In the morning I listen to a podcast, but in the afternoon I just walk and let my mind wander. By the end of the day I'm usually too tired to continue in the focused mode of thinking, but sometimes I'm still able to discover some new insight while walking in the unfocused mode.