Disillusionment is defined as “a feeling of disappointment resulting from the discovery that something is not as good as one believed it to be”.

Disillusioned is defined as “to free from illusion; also :  to cause to lose naive faith and trust”.  

This implies that the desire was not real, the end point was just an illusion or that while it might have been real, one only  had superficial faith or trust in either its attainment or  in ones ability to attain it.