It happens to just about everyone.

A small item such as a set of keys, a coin, a card, an earring or a pen is knocked off a surface. It's assumed that object has landed on the floor where it can be easily found.

Maybe it caught some air and drifted a few feet away. Maybe it bounced and could even be heard heading in a certain direction. 

When you bend down to grab it, it's nowhere to be found. You get down on your hands and knees. You look under the chair, under the table, in the vent, under the nearby rug, in the cat's water dish.

But it's gone. Inexplicably, unbelievably, frustratingly gone. The item might reappear at a later time. Or simply vanish from your life forever.

This is referred to as "Disappearing Object Phenomenon."

Author Tom Jinks explores this topic in his book, "Disappearing Object Phenomenon: An Investigation," released Oct. 14, 2016. In it, he credits paranormal writer and researcher Mary Rose Barrington for giving the phenomenon another term: "Just One of Those Things," also "JOTT" or jottle.

Robert A. Charman, a member of the Society for Psychical Research and the Scientific and Medical Network, reviewed the book on spr.ac.uk, the website for the Incorporated Society for Psychical Research.

"After years of personal investigation into these claims Jinks decided that these unexpected, inconvenient and unwanted object disappearances, reappearances and so on could not be attributed to forgetfulness, unaware misplacement, faulty memory, inattentional blindness or perceptual blindness while thinking of something else to an object in plain sight, hallucinatory error, deliberate deception by themselves or someone else, fugue states, altered states of consciousness and so on," Charman wrote. "What was being repeatedly and independently described seemed to be a genuine phenomenon despite being considered as completely impossible as far as science and everyday common sense is concerned." 

Stephen Wagner on liveabout.com notes that absentmindedness or distraction could be the cause of the Disappearing Object Phenomenon. Some blame poltergeists or spirits when things disappear or reappear, although it could also be psychological phenomena or dimensional shifts.

"The existence of dimensions other than the three we jostle around in every day is theorized by science," Wagner writes. "Sometimes referred to as 'other planes of existence' by the more spiritually minded, these dimensions are sometimes thought of as places where spirits and other forms of reality might reside. Could the temporary invisibility or movement of objects be explained by their slipping into another dimension? Is there some kind of dimensional or temporal shift to blame? It's a pretty far-out notion, but then a genuine DOP experience is hard to explain."

It's a bit like calling a loved one only to get the busy signal because that person is calling you. Or when you text, "Hi Mom, I'm home from work, how are you?" and instantly receive a message from her that says, "Hi sweetie, are you home from work yet? How was your day?"

That's synchronicity, another element of the unexplained.

Coined by psychologist Carl Jung, synchronicity is when coincidence and significance collide. It can take shape through dreams, chance encounters, numbers and other events. Psychology Today says synchronicity and serendipity are primarily psychological phenomena. If they're not noticed, they don't exist. 

What about premonitions that come true? Or déjà vu, that sense of having been somewhere, seen something or uttered the exact same words in the same setting?

"This experience, known as déjà vu, is one of the most common yet mysterious phenomena of human consciousness," according to an article exploring the hidden physics of déjà vu on sciencenewstoday.org.

"Roughly two-thirds of people report experiencing it at some point in their lives, most often in youth or early adulthood," the article states. "It is not tied to culture, education or belief — it seems to arise from something fundamental in the way our brains and perhaps even the universe itself is structured."

Disappearing objects, synchronicities, inexplicable memories and sensations.

Mysterious, yes, or in the words of William Shatner, "Weird ... or what?"