You ever see a dog that’s got its leash tangled the long way round a table leg, and it just cannot grasp what the problem is or how to fix it? It can see all the components laid out in front of it, but it’s never going to make the connection.
Obviously some dog breeds are smarter than others, ditto individual dogs - but you get the concept.
Is there an equivalent for humans? What ridiculously simple concept would have aliens facetentacling as they see us stumble around and utterly fail to reason about it?
I suspect that colonizing Mars (or wherever else) will turn out to be much more than just an engineering problem. If we get things like food, water, atmosphere, and even gravity right, I think we’ll still find an endless list of requirements that we didn’t know were requirements… and some mystery problems that don’t seem to have any cause at all. Those problems will be because of factors we never thought of, or don’t even know how to detect.
There could also be surpluses/deficiencies in our diet or environment that will take years (or perhaps generations) to show up. Again, that would be because of unanticipated, and maybe unsolvable, problems.
I could still see people trying to make it work for generations for some reason, many early colonists in the West died before stable states could be founded.
We for sure will need to exercise, because low gravity turns our muscles into mush.