Some people call it dirt. Other people call it soil. But one way or the other, in the absence of manmade structures, we usually find outselves walking on it. Of course, sometimes it is covered with vegetation and other times it may be saturated with water, in which case we might call it mud. However, it is unavoidable that when we spend a lot of time traveling by foot in wilderness area on dirt trails, that we become dirty. Sometimes it's worse than others, but dirt has a way of working its way into shoes and onto the feet and lower legs, with the socks winding up absolutely filthy in the process. Often along with dirt, grass seeds wind up attaching themselves to socks, shoes, and pants. In fact, getting socks clean after a particularly dirty hike can be a lot of work. Some people even just throw a pair of socks away after such a hike. And life in general can often be that way in one way or another, as the song says:

Some things are unavoidable
Some things are blessings mixed
Some things will always be that way
Never to be fixed