We think all the time, whether we like it or don’t, it’s what we do, this is just who we are. Thinking is the mind searching, questioning, trying to make sense of things it sees. Our mind never goes quiet; it keeps on trying to understand. A thought is what’s left behind, after all that movement, after investigating the world, just a small fragment of sense, something to understand all the thinking. They carry memories, fear, desire and doubt. They are more than a single idea; they are echoes of mind’s attempt to understand itself. 

As said, Thoughts are the remnants left behind after thinking has moved through us. Sometimes it’s just a spark, a small insight into things we think about. Other times it settles in our mind, and it stays, it repeats and it keeps on growing heavier and heavier until it starts shaping how we see the world around us. If we let a thought linger too long, it starts to shape everything we see, hear, feel and believe, over time it becomes a filter, a lens, a quiet force guiding our decisions without our awareness, whispering the same fear over and over, again and again until it becomes a part of our identity, before we realize it, a single lingering thought has become a defined piece of our personality.

“We become what we think about all day long.”
~ Ralph Waldo Emerson

Imagine a river flowing across a landscape, that’s our active mind, always moving and exploring, every thought that lingers is like small rocks that the river leaves behind. Normally, the river would move them along and they won’t make a permanent mark, but if the river keeps following the same path for years, it starts carving a canyon into the earth. Similarly, a thought that keeps circling in our mind, starts shaping our perception of reality.

Just like a canyon isn’t permanent, well, at least in a geological sense, a thought isn’t permanent either, no matter how deeply they seem to carve themselves in the mind. By noticing our thoughts, questioning them and allowing our attention to move on other matters, we can stop a thought from becoming a canyon in our conscious mind. 
Life provides us with new experiences, and fresh ideas just waiting for us to explore them, to reshape our landscape. Even the thoughts that feel heaviest and unmovable, can be dissolved with awareness. A thought only has power if we let it stay, and when we move, the mind moves with it.