PSG has lost in the League Championship 1 against Lyon on a score of 1-2. It was the first setback after 27 days without defeat with 73 points to the meter.
This defeat is particularly dangerous for Paris, as statically speaking, after a long series of wins or games without a loss, a drop is likely especially if the team not relies not quickly (when the next match). An end of series creates a mental relaxation, a frustration which can put poorly a team.
Recently the Real Madrid of Carlo Ancelloti can attest. After a start in La Liga with a long series of victory, the Real de Madrid collapsed.