Reasons we believe

I'm just curious about this so I figure I'd throw this question up in the air.

If you believe that UFO's are extra-terrestrial craft, is it because of

1. You just want to belive

2. You think it's unreasonable to think that "we" are the only ones

3. You had an experience that burned an image in your mind that will never go away.

For me it's 3.

If you have another reason, feel free to ad to the list.