Help me clarify max ratings and microcontroller pins tolerance
MCU pins have clamp diodes on the pins to protect against static discharge (ESD). They work by clamping the pin voltage to the power supply rails. However, they can only handle so much current. If whatever you are driving the pin with itself only has limited current capability then it might bog down and be unable to drive enough current through these diodes to damage them.

One method that is sometimes used is to add in a series resistor to limit the current that flows through the diodes. It plays the same role as the output impedance in the schematic below. It drops the excess voltage across the resistor rather than the nearly constant forward voltage drop of the diodes which in turn limits the current that flows through the diodes. This lets the pin safely clamp much higher voltages. I don't recommend it though...I always add external clamp diodes rather than rely on the MCU's internal ones for such a thing.







simulate this circuit &ndash; Schematic created using CircuitLab