The feet are always on the ground. Still, people say - "keep your feet on the ground". Because it is not literal, it is a saying. A saying which in 2 words means - "be humble".
Often, we feel proud. Maybe our family makes us proud. Or our achievements could make us proud or our good looks. There are many causes of pride. And when this happens we lose our human touch. Our speech loses its simplicity, our heart it's purity. Pride eats away the virtue of the soul. It blackens our deeds. Be human. Keep your feet on the ground.