well to be fair, purely theoretically, you "just" need to accelerate once (and be able to hit the brakes many many many years later!) and find a way to sustain

well to be fair, purely theoretically, you "just" need to accelerate once (and be able to hit the brakes many many many years later!) and find a way to sustain (food, water, air) yourself on a spaceship. Then a colonization flight might very well take serveral hundred to thousands years in the beginning. A bit like the general idea of the recently aired tv show Ascension.