It's amazing how quickly we can make connections and draw conclusions when we are in the right mental space. The fact that these moments can be so fleeting can be frustrating, but it's also a testament to the power of our brain's capacity for problem solving. It's wrong to assume that there's a single answer to why our minds can't always be in that state of clarity. It's likely a combination of many factors, from personal experience to the type of stimulus we have access to.
