Melt 4 tablespoons butter in a large skillet over medium-high heat. Add 4 to 6 thinly sliced garlic cloves; cook, stirring, about 2 minutes. Add 2 1/2 pounds trimmed green beans and a few pinches each of salt and sugar; cook 2 minutes. Add 1/2 cup water, cover and cook until tender, about 6 minutes, then uncover and boil until the water evaporates, 1 more minute. Season with salt and pepper; toss with chopped pecans.