We have known for a long time that the day residue effect exists, but the dream lag effect is a much more recent discovery. What dream-lag research has shown is that we tend to dream of waking life experiences in a roughly circaspetan pattern: that is, we dream of the experience on the first night after it has happened, and then again about a week later. When we dream of it the second time around, it has become more abstract. This may relate to how dreams help us to integrate new experiences during sleep over time.