Have you ever wondered about how many absolutely different, unexplainable species of life, incomprehensible for human mind, defying any of its theories about evolution and organics, are out there even at this very moment?
Creatures that have the capability of local teleportation just by manipulating the atoms of surrounding matter by the telecinetic power they possess.
Species the cell structure of which is so rigid and versatile that they can restructurise and adapt to any kind of environment on a whim, evolving afterwards in a matter of minutes and not millions and millions of years.
Silent, cowardly, peaceful invisible life form, which, if someone disturbs them, forms and spews out a cloud of microscopic organisms, upon inhaling which they crawl unnoticeably towards the brain and restructure the brain cells and their neuron links so that the creature becomes friendly towards that invisible life form, without being capable of thinking about any hostility towards it ever again, whether or not it meant to do so.
Creatures transforming photons into energy for their bodies and accumulating it within them, having no need for sleep whatsoever and having enough endurance to last being awake for centuries on end.
Not to mention, of course, beings with intelligence so vast even most powerful supercomputers ever created by humanity will absolutely pale in comparison.
How, 'how' can one look at all these galaxies, with all these QUADRILLIONS of worlds even on this one photo, keeping in mind that EACH of the stars can house a whole planetary system, quite possibly with even more planets than the Solar system has, with EACH of the planets possibly surrounded by dozens of satellites, some of which can themselves be the size of a planet, have an atmosphere and being a house for a sentient life by itself?
How can one, even with all that in mind, so surely, so confidently say "NO, WE ARE THE ONLY SENTIENT SPECIES IN THE UNIVERSE"?
How ignorant can some humans be.