The trail to the falls
One of the reasons given by the people in my group for not going to the falls was the intent to get to the Koʻolau summit (Loren). Another reason is that the trail down would be too mucky and slippery. But the trail was much nicer than I remembered it, apparently due to Boy Scouts working on it. Perhaps I am confusing it with Malaekahana.(David suggested mosquitoes as another reason not to go down, but I didn't see a one.)