It turns out, from what I can tell, that the reason your glasses get harder to see through, is that globs of sebaceous oil somehow leap from your skin to the inside of your glasses. Those oil globs then prevent light from going directly through the glass, creating the streaks that I am constantly seeing. Which is why you need a glasses cleaner that dissolves oil, not just water and toilet paper. Though, water can be very important, because tiny salt crystals will absolutely scratch your lenses if you rub them around.