You're right! And until last week, I was going out occasionally to the grocery store because I was being careful. Plus, as you say, packages come into the house, so it's impossible to totally quarantine.
And then I went to the grocery store, and five days later I came down with an upper respiratory infection.

Of course, you can imagine what I worried about!
Fortunately, it was only (only!) pleurisy. I have a wonderful pulmonologist. She sent me to the hospital (the hospital! eek!) for a chest X-ray, she saw me in her office EARLY the next morning, before any other patients arrived, she listened to my chest, she confirmed that it was only (only!) pleurisy. One week, and lots of prednisone, later… and I'm on the mend.
But. Now Mr. PG and I are banned from all outside-the-house errands other than outdoor walks. We just can't take the chance with my health. And when packages come to the house, they get opened
outside and the boxes go
directly to recycle. Then we wash our hands for a hundred years.
But of course we're older, and I'm at risk. I don't know that everyone has to be that careful. We're just following my doctor's orders. And I feel much calmer, now that we have a good plan to keep me healthy.
I think everyone has to balance what feels safe with what feels do-able.