How much of a national park do you feel you need to see or understand to feel you've "done it"? Does it depend on the type of park unit?
Some people plan their trips out West to do a national park a day.
Others can spend a week in Glacier National Park or Grand Teton National Park. When they come home, they know that there are so many sections of that park that they haven't seen that they feel they just have to go back there.
If I visit a national historic park or monument like De Soto National Memorial, I focus on why it became a park unit. But it's more difficult with larger iconic parks.
Knowing that you've done a park is very subjective. It's probably somewhere between walking all the trails in the park and going into the Visitor Center to get your National Park passport stamped.
So how do you decide when you've really "done" a park?