In the chapter A Journey in the Dark, Pippin drops a loose stone down a well and an angry Gandalf responds to this by calling him a fool. But was Pippin truly a fool? Let's look at the evidence. Before dropping the stone, Pippin is attracted by the well. Here we can see that the well is acting on Pippin, either by pulling him closer or by implanting the desire to come closer. How this is achieved, we do not yet know, but things will become clear soon for upon looking over the edge, Pippin is struck in the face by a chill air rising out of the well. In folktale, myth and religion, breath and wind are associated with spirits, and a cold wind rising out of the dark depths implies spirits of the dead rising up from the underworld. A similar chill wind is felt by Frodo on the Barrow-downs, as he desperately searches for his companions prior to be captured himself by evil spirits from Angmar who have inhabited the corpses buried there. Later in The Passing of the Grey Company, a chill wind like the breath of ghosts comes down from the mountains. This suggests an association with cold wind and the spirits of the dead which by itself doesn't necessarily mean that Pippin was spiritually attacked by a ghost, but given that something drew him there it certainly suggests that it is possible. The final piece of evidence is Pippin being moved by a sudden impulse. Once again something happened to Pippin. A positive echo of this event happens to Pippin when he and Merry are being held by the Uruk-hai. First in the unbidden vision of Aragorn tracking them and secondly in a sudden thought leaping into his mind to leave behind a sign for his other companions. In both cases, the vision and thought happen to Pippin, perhaps as if coming from without. Given all this evidence, I believe a case can be made for Pippin being the victim of spiritual guerilla warfare rather than a so-called fool.