When you're halfway, you're at the middle point of something. If you pause to catch your breath halfway up a hill, you still have half the hill left to climb.
You can make it halfway along a marathon route, or 13 miles, and you can also make it halfway through your book before you fall asleep. You might only make it halfway through an enormous slice of cake, or halfway through math class before you start to nod off. A halfway house, originally an inn between two cities, but today it's a place where released criminals or recovered addicts can live while they get back on their feet.