As the story in Theodore Taylor's The Cay develops, we see that Henrik van Boven is not a true friend of Phillip but rather a superficial friend, the sort of friendship developed that never lasts. Henrik is not a true friend because he does not protect Phillip's best interests. In contrast, Timothy turns out to be the best friend Phillip ever knew because, while alive, Timothy not only protected Phillip but helped him grow as a person.
We first see that Henrik is the sort of superficial friend who doesn't protect others' interests when we see that, after the torpedo bombing, Henrik still influenced Phillip to play with him at the fort. Phillip had been ordered by his mother to stay close to home that day, but as soon as she was distracted, Phillip "stole away down to the old fort with Henrik van Boven" (p. 11). More importantly, Henrik does nothing to protect either himself or Phillip but rather encourages Phillip to play where it could be dangerous. Had Timothy been in Henrik's shoes, he would have encouraged Phillip to stay home. In addition, when Phillip learns his mother wants to leave for America, Phillip reflects that "Henrik and his mother would think us cowardly if we left just because a few German submarines were off Curacao" (p. 20). A true friend would never think another person cowardly but rather acknowledge it is okay to be afraid.
In contrast to Henrik, Timothy demonstrates true friendship by helping Phillip learn to cope with his blindness by helping him learn how to move around the island and do things on his own. In contrast to Henrik, when Phillip feels brave enough to try and climb the coconut tree, Timothy stands underneath, ready to catch him if he falls and calls up to him, "'Tis no shame to ease your own self back down to d'san'," which is Timothy's way of telling Phillip that there is no shame in being afraid, especially when Phillip has put in his best effort. According to what Phillip says about Henrik, it is unlikely Henrik would have said the same wise, caring, and compassionate remark. Most importantly, Timothy sacrifices his life to protect Phillip from the severest blows of the hurricane, something Henrik never would have done.
Taylor contrasts the two friendships to develop the central theme that true friendship is colorblind, nurturing, and even sacrificial.