What does it mean to "not internalize" accomplishments? Basically, not being able to integrate achievements and assign value to yourself.
Typically, these are cognitive distortions and negative thought patterns. Much of the time, "Imposters" feel lucky for their success, not necessarily competent or confident. In fact, There is an ever present fear of being found out and exposed as a fraud. These feeling serve to drive anxiety, fear, and more doubt. Fear of failure, making a mistake or not knowing something makes this cycle of anxiety and sometimes depression worsen. If you would like to view an article about Imposter Syndrome, click on this link: NY Times Article.
Doubts and fears can arise due to the notion that if things come to easily, the tendency is to discount the value of the process which lowers self-esteem and increases the feeling of being an imposter.
One last observation, confidence is the ability and recognition that you can "do something." Self-esteem is how you "value" what you do or the attribution to it. Getting an award, promotion, or achieving some goal is essentially discounted with thoughts like, "I don't deserve it", "I could have done better", "Someone else is better than me." Correcting the Imposter Syndrome means confronting your fears, negative self-talk and the way you value yourself. Work on validating and affirming yourself and accomplishments. Learn to accept compliments and make yourself an MVP of your own life.