One reason is crowds. If I'm checking out all of the people, trying not to bump into them, I find I can't look at the shelves at the same time.
Which brings me to my second gripe: I'm too short to see or reach what's on the top shelf. I'm not kidding when I say that back in the days when I could lift my son, I would lift him over me, and have him grab what I needed. Eventually, I grew a spine, and now I ask for help.
Finally, I've discovered that lists are only as good as the people composing them. If you forget to put something on the list (like I do), then chances are you will not get it, and you'll be angry with yourself when you get home to discover your mistake. That's assuming that you even remember to bring your list.
Suffice to say I have trouble doing little things right now. I really miss my brain.