My wife finds it interesting that I never notice when she cuts her hair (subtle trim).
From my perspective I'm not sure that never is completely accurate, but it may be close.
I am reminded that she notices when my hairs are cut.
Although, she hasn't noticed on the couple of occasions I've shaved my stache.
It is not that I'm totally clueless to her appearance, I compliment her dress and much to her chagrin I have noticed an increase in gray (which brings angry denials).
Turns out there's a really good explanation...
'Hair blindness' likely to exist in humans
New research hints that human brains process hairstyles distinctly from other facial features. And just as a small proportion of people have trouble recognising faces yet otherwise see normally, others probably experience hair blindness.
It's not my fault and the scientific community is united in that fact!