I think that it is clear that fear and insecurity is a major theme in this book. Just look at what Crusoe does right away when he finds himself on the island.
After his first night up in the tree, he starts to build himself fortifications. He spends so much time on this -- without many tools he pounds stakes into the ground in a half circle that is 8 yards deep and 16 across. That's a huge amount of stakes!
Later on, he plants all those trees in front of his home to make it impossible for people to approach. He makes himself his "country home" just in case and then he starts using that cave as well.
On the other hand, you can argue that he's pretty bold with regard to people. After all, he gets himself all ready to go and try to kill 20 cannibals before he talks himself out of it. And he really does kill a group of them with Friday's help.
So fear is not the only thing going on, but it certainly is important.
Like most human beings, Crusoe is scared witless when he arrives on a deserted island and is frightened of every shadow and every gust of wind. He is obviously not well prepared to survive on his own, but as he grows in his abilities and his comfort level, he begins to assert himself. He eventually overcomes his greatest fear or challenge when he finds out that "the devil" is actually just a goat and from that point on is able to move about free of the fear that kept him prisoner for so long.
yes, fear is a major part of it... just look at how he thinks about the footstep he sees in the sand halfway through the story... he immediately talks about canibals/savages/brutes... but it takes some time before he actually sees skulle on the beach... i mean, wouldnt it be understandable if he actually wanted to meet someone else after I dont know how long (say 15 yrs) on the island... he is so afraid of these nonenglishmen that he actually builds a fort around his place and is prepared to die on his small island, before trying to make contact... typicall colonialism