For us to exist, a number of events had to occur:

1) There had to be a "big bang," a singularity (which is a fancy term for "we don't know how it happened"), capable of producing a universe (out of, presumably, an exceedingly large number of universes) comprised of particles which had the right spins, masses, and velocities for the emergence of life. As for those supposedly-existing other universes, which might or might not have particles with the right spins, masses, and velocities for the existence of life -- do they even have particles? Or spins, masses, and velocities? Nobody knows.

Our purview of the universe, moreover, is conditioned upon our existence -- this is the idea behind the Anthropic Principle. The universe is arbitrarily like this because we are here.

2) There had to be a planet Earth, a planet with the right mass in the right vicinity of a star of the right mass and age. There probably also had to be a collision of some sort -- since there also had to be appropriate conditions such as the existence of continents and oceans, the right amount of tidal pressure, an appropriate axial tilt, and so on. Perhaps there is life elsewhere in the universe, but it's hard to imagine that much of extraterrestrial life subsists in the harmonious conditions necessary for evolution. After all, life existed on Earth for more than three billion years before the Cambrian explosion which made possible the genetic diversity we see today. Before that time, 541 million years ago, there were some unpleasant-sounding periods of natural history -- the Cryogenian for instance. Icecube Earth was probably not a promising scene.

3) There had to be an appropriate process of natural selection, including "great extinctions" destroying old life so that new life could flourish, eventually producing intelligent life and conditions in which intelligent life would not be driven to extinction. It's quite possible the Great Dieoff and the extinction of the dinosaurs were necessary for our existence.

4) As an intelligent species, we had to develop equipment such as bipedalism, opposable thumbs, and complex language if we were to be able to make intelligence epigenetic (i.e. capable of learning from experience). It's hard to imagine our understanding of the universe having developed to the level it has without these things.

5) We had to become an environment-making species (this in itself is not unusual -- beavers build dams, bees build hives and so on) in such a way that we could create the basic tools of what we call "civilization," thus preserving our complexity and numbers as against the forces of natural selection. In understanding this phenomenon it's important to know that most of the human species' 200,000-year existence occurred even before what some authors are calling the "cognitive revolution," never mind, say, agriculture, or industry.

You can see, then, that the process by which the universe developed us was and is characterized by a great number of freakishly uncommon and unlikely phenomena, and that if even some of these phenomena had not occurred, we would not be here. Think of your existence, then, as an accident made possible through the sheer vastness of the multiverse.

Thus even if the odds are against the human species' saving itself from extinction by out-of-control social processes (like, say, capitalism, with its abrupt climate change), we can always respond to the sort of pessimism we hear from doomsayers with the standard reply: