Closed-loop or cosplay

Open-loop demos are fine for a desk. They are not a control system. If your robot drives until a timer expires and hopes the table edge is still where you left it, you built a ritual.

Name the controlled variable

Write down the quantity you care about: heading, wheel distance, arm angle, line position. Then name the sensor that measures it. If that sentence needs a shrug, stop coding and fix the sensing path.

Log before you tune

Tune with data. Log setpoint, measurement, and output at a fixed rate. A PID that you only watch with your eyes will absorb your optimism. The log will not.

Fail closed, not mysterious

When a sensor drops out, the firmware should enter a known safe state — stop, coast, hold — and say so. Silent freezes teach operators that the robot has moods.