Hello Tim,
Spudman has the answer as far as I can tell.
From what I have learned over the years, if you ever notice the arms of some wooden chairs, (grandma's rocker maybe) the area around your door knobs on your doors and other places where your hands and fingers touch are sort of sticky. This is from the oils and acids in our hands and fingers which tend to eat into or soften the paint or especially varnish on the doors and what not over time. This also happens on our guitars. I think the newer poly coatings are less troublesome but the other finishes tend to get soft with the oils and acids in our hands.
I wrestle with this every time I go to paint a darn door in the house, the area where our fingernails hit around the knobs chips off the paint because I didn't clean the oils from our hands off good enough before I painted it the (last) time and the paint is not adhering very good.
Just some thoughts IMHO.
M29