There is no UFO and also there is no alien.. at least not in common minds and references.

If I tell you that I have seen the alien, you won't believe me, or at least you will ask for my explanation. If I explain to you in my understanding, more questions will raise in your mind. Eventually, you have to see them yourself and perceive the experience with your own understanding. After that, you will feel eager to tell people about it.

The day when the alien invade planet earth, human civilization will experience chaos. The first thing we have to do is trying to accept the sudden change in the reality. By that way, we will lessen any disadvantage caused by shocking event.

As long as we think that the animal races were lower than us and were not a form of civilizations, our minds will always reject to believe a concept of the existence of alien races which far more advanced than human civilization.

If you really want to see the alien, then I will tell you how they can be seen. First, you will have to find and face something in yourself which you fear most. Second, if you can overcome it, then you will begin to see their true appearance.

You can not coerce common people to believe in alien existence. The best effort you can do is to have them know and think about it.