The things you have mentioned though are easy, birds evolved towards flight hundreds of millions of years ago, the answers on flight just required observation and planes are actually very simple things. Travelling across space though is just different and the physical problems are immense.
We can forget travelling beyond our solar system, that will always remain physically impossible unfortunately unless our understanding of physics is wrong. Aliens face the exact same physical problem which is why they cannot exist in the advanced form that science fiction dreams up. If they are out there then where are they?
https://en.wikipedia.org/wiki/Fermi_paradox
Even for Mars getting there is relatively easy and we've already done it with unmanned missions but getting there and surviving there as humans is another level of hard. The longest that anybody has survived in space is around 1 year and that's with the knowledge of being able to come back anytime.
With Mars it takes 1 year to get there and then they'd have to wait 1 year for a window to come back, and then it would take another year to get back.... The problem is vast. They won't be in the ISS for that year either, they'll be in the equivalent of a capsule as big as your lounge with all the stress of not being able to escape, and nothing can go wrong.... On a biological level we can't mentally and physically live in that environment for very long.
I'm by no means a skeptic but there are some things that we will never be able to understand.