It is normal to think that way that a particular club will win their opponent just because we feel that such club is better than there opponent  and again because of their current form also the team they have been able to defeat in the recent time may make us to conclude that they'll actually win but we forget so soon that the club they will be coming in contact with has a history when it comes to playing finals, I think many people were too sure of PSG because of the reasons I stated, another thing is sentiment, football is a practical thing, it is also a game of uncertainty, we can never be sure of anything unless the game is over, why Chelsea playing like that is because they came prepared, if you look at their play pattern, you'll understand that everything was planned, they came in and keep forcing attack and before we could know it it was 3:0 against PSG, that was when PSG became more confused and very other thing was history, so congratulations to Chelsea for a well deserved victory.