is it not possible to say "realize" in terms of "make it happen"?
Yes, I think so. You could say that somebody has finally realized their ambition, plan, dream, or whatever.
yes, in English "to realize" means to carry out to completion.
what does this sentence even mean?
Where does "complete" come in?
In my dictionary 'realizar' = to achieve, to carry out, to make, to undertake, to realize. I think 'complete' is pretty close to 'achieve,' if that is the question