I would contend that you haven't really grasped the sheer scale of the universe if you think space travel or colonization is even remotely possible. Sure we went to the moon once but it took pretty much all of our might coupled with gobs and gobs of money. We will surely be back at some point, and I think it's inevitable that some humans will at some point travel to mars, or one of the moons of Saturn/Jupiter (on what will assuredly be one-way trips), but that's it. Forget about even attempting to reach our closest neighboring star; our current understanding of physics ensures that we would never be able to make that trip. Same reason we're not hounded by alien tourists all day every day even though the universe is teeming with life, those other instances of life are equally locked to the respective places where they spawned, which brings us to the next point:

Life. Yes, earth-based life is very resilient, on earth. Consider the massive, incomprehensible planetary forces fighting it out for billions of years until some semblance of a stable -but incomprehensibly unique- balance was reached, where life was finally allowed the necessary time to thrive, flourish and diversify around that very particular balance. Take life out of the environment in which it developed and it fizzles out very quickly. 99% of the effort in any kind of human space exploration would be on trying to replicate earth's environment to a ridiculous degree of precision and then hope/pray that nothing ever breaks on any of the systems/machinery/technology you use to replicate earth, because then you'd be SOL and fizzle out quickly.

Here on earth we've got gargantuan industries (just to name a few think about electronics, plastics/petroleum, metals), built piece by piece over hundreds of years in all material sciences, mutually interacting and interdependent, with massive and incredibly specialized supply chains that rely on readily available amounts of very specific resources that you can get on earth. You can get a plastic ring seal, any size of nut&bolt, and a microcontroller here on earth for $1. No amount of money will get you any of these out there in space. We only manage this for the ISS because it is pretty much tethered (at a distance of only 400km) to a huge-ass planet that can source and produce anything it could ever need, put it on a rocket (costs a lot of money but can be done on demand) and have it get there in a matter of hours, and even then it's very specialized, technical and perpetual effort to maintain it.

I can see us maybe pulling that off for something built on the moon (our backyard, really) but for Mars, our closest neighbor? No chance if you want to have actual humans involved, only machines and very slowly over hundreds of years, if at all.