Actualisation was a term coined by Abraham Maslow back in the 1940's . He felt that once people's basic survival needs are met, so their desire to grow in mental and emotional dimensions increases. Carl Rogers the founding Father of person centred counselling took up the idea that just as a plant grows towards the light we human beings grow and change according to how positive and constructive our environment is and this of course depends entirely on our own subjective idea of what constitutes positive/negative - one man's meat is another man's poison.
In the best possible of worlds each individual would be able to fulfill all of their potential as a human being but unfortunately we do not always experience a world which is entirely nurturing, safe and accepting of individual difference
and a lot of energy can be taken up in either maintaining a sense of self or defending a sense of self
A sort of distortion of this powerful tendency to actualise starts to happen and we may begin to feel out of step with ourselves or incongruent in some way. Talking with a counsellor can really help these distortions to become clear and bring clarity to any feelings of being alienated from ourselves