People make associations, strange mental linkages connecting one subject to another. The smaller connections make sense sense (peanut butter/jelly, tuna/mayo, Sinatra/smooth, etc.), but the mental chains of association are never short. The brain's chains are forged of thousands of links, most of which the brain's owners don't even understand (white bread/loneliness, water ice/laughter, a capella music/nostalgia, etc.)
If you try to dig deep and analyze each and every link, you might make sense of these long strings of unconscious thought. But you probably won't.