You are walking down a path in the woods, thinking about an upcoming business trip you are taking, and you see a snake on the ground. You freeze and jump backwards. Your heart starts racing. You are ready to run away. But wait, it’s not a snake. It’s just a stick. You calm down and keep walking on the path. You noticed the stick, and even responded to it, in a largely unconscious way.

https://www.blog.theteamw.com/2011/04/03/100-things-you-should-know-about-people-98-attention-is-selective/