What is the psychological impact of big footprints on Robinson, and what is the purpose?

The big footprints caused Robinson's inner panic, reflected Robinson's inner fragility living on a desert island, and laid the groundwork for later encountering savages.

Robinson lived alone on the island 17 years later, one day, he found a human bone on the coast of the island, which had been burnt excessively. It turned out that a group of savages from outer islands held a feast of human flesh here. Robinson was frightened. Since then, he has increased his vigilance and paid more attention to the things around him. Until the 24th year, another group of savages came to the island, ready to kill the captive. Robinson found and rescued one of them. Robinson named the rescued savage "Friday". From then on, "Friday" became Robinson's loyal servant and friend. Then Robinson took Friday to rescue a Spaniard and Friday's father. The Spaniard told Robinson that there were more than a dozen Spaniards in the indigenous tribe and asked them to join the island together. Soon an English ship docked near the island, and the sailors on board rebelled and abandoned the captain and other three people on the island. Robinson and Friday helped the captain subdue the sailors and recapture the ship. He left the sailors on the island and left the desert island for England with the captain on Friday. By this time, Robinson had been away from home for 35 years. He got married in England and has three children. After his wife died, Robinson went out to sea for business again, passing through the desert island where he lived. At this time, the sailors and Spaniards who stayed on the island have settled and multiplied, and there are many cattle and sheep. Robinson also sent new immigrants, gave them the land on the island, left them all kinds of daily necessities, and told them that some Spaniards would come to the island soon, and left the island without discrimination. Robinson stayed on the island for 28 years and 2 months 19 days. Seven or eight years later, Robinson returned to the island with a bunch of necessities of life on the island and visited the Spaniards and sailors.