Docking with the ISS may seem simple. However, actually doing so shows how difficult orbital mechanics can be. It's like traveling down a highway at 28,000 km/hr (17,000 mph) and parallel parking in an open garage on a multibillion-dollar laboratory traveling at the same speed. If you try to accelerate forward, you actually drift up, and there's no air friction to naturally slow you down. Oh, and if you hit the lab, everyone aboard both your craft and the station dies, and the resulting debris field could wipe out dozens of satellites and even harm people on the ground. No pressure, obviously.