Obviousness is the quality of being obvious.
It might not be obvious that what seems obvious to you might not be obvious to other people, e.g. students, colleagues. For example, you might pick up a lesson plan and realise it's obviously PPP, but your colleague might not. Similarly, it might seem obvious to you that he, she and it conjugate verbs with the third person -s, but to many students it won't be.
Focusing on the obvious is an obvious way of looking at any issue, particularly if the students don't find it so obvious. Not focusing on the obvious can leave you missing the obvious, which obviously isn't a good idea.