Why soft bodies are hard to control precisely
A rigid robot arm has a fixed, well-defined geometry, so engineers can calculate exactly where the end of the arm will be for any given joint angle, a well-established branch of robotics called kinematics. A soft robot doesn't offer that convenience. Its body can deform in an almost unlimited number of ways, bulging, twisting, or bending unevenly depending on the load it's carrying, the surface it's pressing against, and the material's own elasticity, so there's no fixed set of joint angles that fully describes its shape at any moment.
This makes soft robots substantially harder to model mathematically and harder to control with the kind of precision a rigid arm achieves routinely. Engineers often rely on approximations, embedded sensors that estimate the actuator's current shape, or control strategies that accept some uncertainty rather than demanding exact positioning. It's an active and unresolved area of robotics research, not a solved problem with an established textbook answer.