Your encouragement gives them the courage they need

 Encouraging words build the courage they need. Pointing out someone's weaknesses will only make them weaker. Pointing out someone's strengths will make them build on the strengths they have. 

  If you come at someone harshly they close their ears so they can't hear you. Even if later you try to give them encouraging words, it will fall on deaf ears because they already shut you out.

  Berating someone else does nothing but have a negative affect on them and you. But encouraging words will have a positive affect on you both. 

  If you want to comfort someone after a negative situation you definitely can't say I told you so or you should have known better. You won't comfort them if you point out the things they did wrong.

  If you want to encourage someone it is only possible if you give them words of encouragement.