Have you ever lost something, only to find out it was under your nose the whole time? If so, you were being imperceptive. Imperceptive means "unobservant."
The word imperceptive is built from the prefix im-, meaning "not," and perceptive, meaning "able to discern or understand." While a perceptive person notices the subtle hints and details around them, someone who is imperceptive may overlook even the obvious. The word is often used to describe someone who misses social cues or details. So if you’re imperceptive, you might need a friend to point out that your shirt is on inside out — again!