An analogy is instructive here. If we glue one object to another, it will adhere. If we remove it, it will leave behind a small amount of residue; the longer it remains, the more residue is left. If we take that glued object and stick it to several places repeatedly, it will leave residue everywhere we stick it, and it will eventually lose its ability to adhere to anything. This is much like what happens to us when we engage in “casual” sex.