What miraculous skill does Ishmael have one afternoon that he is never able to repeat? (Ch. 7)

Ishmael climbs a coconut tree.....

"It is difficult to explain how it happened, but I mounted the coconut tree quite fast and unexpectedly. By the time I realized what I was doing and thought about my inexperience in this particular art, I was already at the top of the branches and plucking coconuts. I climbed down just as quickly and looked around for something to crack them with."

"I got up well rested and thought, I think I have enough energy now to climb and pick more coconuts for the road. But it was impossible. I couldn’t even climb past the middle of the trunk. I tried again and again, but each attempt was more pitiful than the last."