Leaving the solar system isn't difficult. One of the Voyager Probes has already left the solar system and Dala says the other one is pushing at the fringes as we speak but the situation is "confusing, so don't ask." The real challenge would be getting to anywhere else outside of our solar system and sheer distance is the challenge in every way. That said, in the lifespan of a single man we went from heavier than air flight to the moon landing. The history of travel, all the way back to prehistoric man, is chock full of people trekking inconceivably long distances with the technology they had at the time. Will you see a probe land on a planet outside our solar system in your lifetime? Probably not. Will it happen sooner than any of us expect? Probably.