Player motivation

If my team didn't played well and i said they're simply not good enough or something like that did it give a boost to the team? or the morale will decrease? how does it affect to the team?

That really depends on your players and the circumstances. Some will be disheartened and some will be motivated and it also depends if morale was high to begin with, if the players think you're being reasonable or not etc.

I think there are 2 factors you need to consider - morale and motivation.

If your team is below where they should be in the league then its likely that motivation is high but morale low and vice versa if your team is overperforming. Its the managers job to try and keep both motivation and morale as high as possible but imo the team talks are so unintuative (eg you tell them they can win a game which is close odds and some players look delighted but demotivated at the same time eh? why?) its best to just ignore players untill they become unhappy with your team talks and then just a give a pat on the back to your best player and disappointed to anyone with <5

Ask Fabregas.