A large part of the confusion with ground is due to the terminology associated with another important word: voltage. When someone says, “point A is at X volts,” that wording ignores a key part of the voltage story. Voltage only exists between two defined points, and a better term for voltage is the older but still-used phrase potential difference. Unless you specify the voltage at A with respect to that other point, saying “voltage at point A” may represent different potentials to different parts of the circuit. It’s especially challenging as the various grounds in the circuit – Earth, chassis, and common (signal) – often have potential differences between them and these can range from millivolts to volts and more.
Of course, where there’s a potential difference, there’s a possibility of current flow.