Noticing things is ôdd. You may see something several times, before you notice it. You may need to gather plenty of information and push it around, for a while, before an underlying explaining pattern reveals itself to you. You may need a sleep, or a walk.
As exploratory testers, we have the pleasure of making regular novel discoveries.
When you realise something, an idea has bubbled from your unconsious thought processes into your conscious mind. That transfer is the vital first step in turning incoherent observations into a useful model. For more on this, find wide references at :Dual Process Theory, and deep while accessible science at :Kahneman's Thinking Fast and Slow.