Let them be helpless like children, because weakness is a great thing, and strength is nothing. When a man is just born, he is weak and flexible. When he dies, he is hard and insensitive. When a tree is growing, it's tender and pliant. But when it's dry and hard, it dies. Hardness and strength are death's companions. Pliancy and weakness are expressions of the freshness of being. Because what has hardened will never win.
Why it is hard sci-fi
A guide leads two clients into the Zone, an interdiction area where the laws of physics behave inconsistently. The films rule is that the Zone changes from moment to moment, and the only way through is to throw weighted strips of cloth ahead and follow only the path the strip lands on safely. The science is bracketed. What the film commits to is the Zone as a procedural problem with a working ritual.
Science inside it
Anomalous regions, path-dependent traversal, and the idea that an environment can encode information that resists direct measurement. Tarkovskys Zone predates the Soviet Chernobyl exclusion zone but anticipates the operational shape. You move slowly, you follow the rule, you trust the guide.