The ability to come up with a lot of alternatives is an important Thinkibility skill, reflecting “mobility” in thinking. As all skills, they have to be trained and maintained by exercises. Recently we came across a funny, but existential exercise.
Since the 1950s, scientists have argued the idea that “habitable zones” around stars are the most likely places to find life. Numerous discoveries in these zones since 2007 have generated estimations of frequencies of Earth-like planets —in terms of composition— numbering in the many billions though as of 2013, only a small number of planets have been discovered in these zones. Nonetheless, on November 4, 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs in the Milky Way (Extraterrestrial life).
And yet, we see nothing, hear nothing, and we’re visited by no one.
So where is everybody?
Welcome to the Fermi Paradox.
We have no answer to the Fermi Paradox—the best we can do is “possible explanations.”
The Thinkibility nibble for today is just that. Give us at least 15 “possible explanations” why mathematically there must be extraterrestial life, yet we have never experienced it.
thinkibility 
1. They have a different dimension.
2. They came, and we have records of them already.
3. They came and live among us.
4. There is a God, and we are the only creatures in the Universe.
5. We get to see the other people and places when we are under the influence.
6. Humans have only been around for a short period of time so there may be visitors tomorrow or next week or in a century or in the next 1000 years.
7. The visitors might be microscopic.
8. The visitors might be too big for us to see. We might be what they think is microscopic.
9. Meteorites are not returning to their systems so no one knows we are here although the devices may be getting here they aren’t returning.
10. The communication loop on their end is not able to receive our odd devices. They are still using floppy discs.
11. Disinterest.
12. Oxygen mix is wrong for their species and evolution.
13. The beings from other planets are introverted and don’t care.
14. The beings are too evolved and social to care about anyone this far away.
15. All the other planets have Eden and weeds aren’t part of their experience, and their systems are so healthy they just don’t need to find anyone else.
16. There are too many planets with deserts and difficulties and they are unable to leave because they are working so hard on their own planets/systems to improve.
I like your number 7.
Also, we may be able to create whatever we wish to create (“extra” terrestrial). This is starting to happen in the field of nanotechnology and robotics.
From the space travel point of view, we are right at the beginning. We’re still at the bicycle level.
1. We have not perceived in the way necessary to apprehend.
2. Some can perceive and are not believed.
3. They may exist as concepts or percepts, that are real but unrecognised.
4. They may reveal themselves rarely in some special humans.
5. It may not be necessary to know them.
6. They exist in a form that cannot be imagined yet.
7. Humanity has not reached the point in evolution to understand.
8. Extraterrestrial life is mostly invisible.
9. Most people do not seek extraterrestrial experience.
10. Extraterrestrial life may only be understood when life on Earth is understood.
11. It may be understood through higher mathematics.
12. We may need the will to experience it.
13. It may be too simple to understand; we’re obsessed by complexity.
14. The concept of “extraterrestrial life” may need changing.
15. There may be a time in the far future when humans extend themselves as extraterrestrial.
16. There may be humans already existing as extraterrestrial in other galaxies or universes waiting for us to evolve mentally and spiritually, in order that they communicate and we construct.
17. In recognition of the necessary happiness of others on this planet, and in the creation of universal happiness, the nature of “life” may be come to be understood.
Why haven’t we found aliens? Here’s the bad news, and the good news http://www.geekwire.com/2016/seti-why-havent-we-found-aliens-bad-news-and-good-news/
Hyper-intelligent aliens ‘have already explored the galaxy and visited Earth’, scientists claim
Charlotte Edwards, Digital Technology and Science Reporter
https://www.thesun.co.uk/tech/9893815/intelligent-aliens-visited-earth-scientists-claim/
If Aliens Exist, Here’s How We’ll Find Them?
Conjectures about advanced or intelligent life are shakier than those about simple life. Yet there are three features that may characterize the entities that SETI searches could reveal.
• Intelligent life is likely not to be organic or biological.
• It will not remain on the surface of the planet where its biological precursor emerged and evolved.
• We will not be able to fathom the intentions of such life forms.
Two familiar maxims should pertain to all SETI searches. On one hand, “absence of evidence isn’t evidence of absence,” but on the other, “extraordinary claims require extraordinary proof.
https://nautil.us/issue/97/wonder/if-aliens-exist-heres-how-well-find-them?utm_source=pocket&utm_medium=email&utm_campaign=pockethits