Key word there is "only". Of course science not the only way. To simply observe something, such as that the sun always sets in the west, does not rise to the definition of "science", but it's a perfectly fine way to know many kinds of things. But for acquiring less obvious knowledge, such as that the sun setting in the west is an artifact of the way it rotates around its axis while it orbits the sun in accordance with the natural laws discovered by Kepler, Newton, and Einstein, science has been far more successful than other methods. Especially the more "woo-ish" ones, such as fortune telling techniques, believing in internal "spiritual experiences", or believing in religious "revelation".