I wonder whether some psychological disorders could have been better explained through a concept such developemental instinct and what would have looked psychoanalysis like if Freud considered such a concept.
development of ego strength could mean according to the Freudian model that through angst and anxiety you ego grows, in other words. your pains make you stronger. Every pain you go through adds to your resources.
Successfully resolved conflicts between id and superego makes your ego grow.