Having seen a UFO myself I can safely say that there _are_ aircraft with capabilities far above that what I would expect from our own air force in our skies.
A friend and I witnessed formations of lights sweeping across the horizon making 90 degree turns in the blink of an eye.
There are a myriad of natural phenomena, optical illusions and - dare I say - mental aberrations that could account for one seeing lights in the sky.
I've seen several objects in the sky that I've not been able to immediately explain. Having been 'tricked' in this way and later realising the 'natural' explanations the idea of UFOs being explained as extra-terrestrial is not at all surprising to me.
I once saw what I at first thought was light from a helicopter one night, then it turned a tight angle and shot off toward space. I thought for a second that maybe UFOs were real, then I realized I was close to a military base. There is probably technology in the armed forces so advanced that most people do not know about it.
A friend and I witnessed formations of lights sweeping across the horizon making 90 degree turns in the blink of an eye.
There you go.