I have noticed that almost every person I have asked recently believes extraterrestrial life is likely to exist. For the most part, they cite the Fermi paradox as their reasoning for this belief.
However, the scientific community generally believes in a common ancestor for all life on Earth. Evidence suggest the Earth formed around 4.5 billion years ago and that life emerged about 3.7 billion years ago.
So in the one place in the universe where we are certain that life has emerged, we believe it has only occurred once. Once in 4.5 billion years. Even where the conditions do exist to produce life, it seems to be exceedingly rare. To me, this explains the Fermi paradox and suggests that we may in fact be alone in the universe.