It might also be that the particularly 'good' or 'bad' memories are what stick in your mind the most. After all, people don't really remember days spent cleaning the house, or preparing meals, or other stuff like that. The neutral days, those are forgotten first.

[He sees Xie Lian eyeing that bubble, and in that moment he comes up with an idea.]

Tell me about a good memory. Maybe speaking it out loud will have it at the forefront of your mind, so that'll be the one the bubble shows if you touch it.