The Smart Light That Turns Off Earlier and Earlier

A smart-home system uses AI to save energy.

It learns when people are present in a room.

If no movement is detected for a while,

the system automatically turns the lights off.

At first everything works well.

The residents hardly notice any difference.

But after a few weeks something strange happens:

The lights turn off earlier and earlier.

Sometimes even while someone is quietly sitting on the sofa reading.

The AI only wanted to save electricity.

Yet the lights seem to become increasingly impatient.

Question:
Why can a learning smart-home system start turning off lights faster and faster?

Solution will be unlocked tomorrow.