There are several ways this proverb can be interpreted. A Wikipedia page offers this as one interpretation: People who are always moving, with no roots in one place, avoid responsibilities and cares. This is another example: A frequently replanted tree yields little fruit, meaning those who don’t put down roots ‘yield little fruit’.
However, I view it a slightly different way. Studies have shown that a stone rolling down a hill will pick up small amounts of moss. If the rock keeps moving though, those bits of moss will eventually fall off, and new bits of moss will replace it. The moss will not grow though. So even when picking up debris along the way, there is no need for the moss to stay forever.
I think this is a valuable lesson in life… as we go on our journey through life, we will, occasionally, pick up bits of moss. If we give up, stop fighting, and stand still, the moss will grow. Eventually you wont even see the rock beneath it. If you keep going though, those clingy bits of moss WILL eventually fall off.
That rock, rolling down this seemingly endless hill, will never be completely moss free. There will always be those tiny scraps that try to buckle in for the ride. And when they fall off, they will be replaced by new moss. But while things will never be perfect, learning to keep moving forward, no matter what, will prevent you disappearing behind a curtain of moss forever. Don’t let all the bad stuff, the ‘moss’ to build up and destroy everything you are.