When we are born, we do not have any concept of behaviours, they are shaped through our experiences in life. We collect information, and by the age of six, we gather this information to form beliefs. Many of our core beliefs are developed during our childhood and teenage years. If left unchallenged, these beliefs go on to form our behaviour as adults. Beliefs can be changed. To do so, one must become conscious of their beliefs, and then work to understand, challenge, and change them, which ultimately helps change behaviour. For example, if you are a female who grew up in a house where your father abused your mother, you may have negative views on men, leading to problems trusting and forming relationships. If the same person were to understand and challenge their belief system, they would be able to gradually change their behaviour to form more successful relationships. The task of altering the belief system you formed earlier in life is difficult as these comprise our core beliefs; however, it is not impossible. When you change your beliefs as an adult, these are formed in a less rigid manner, and are easier to challenge, to address any further behaviours. Awareness is key. 
Your childhood affects the way you think as an adult. You subconsciously learn a significant amount in your earliest years, and these experiences shape your values and behaviours. Traumatic events suffered at an early stage in life, can emerge through behaviours in your adult life, through triggers. These traumas can range from PTSD to anxiety, or in more subtle behavioural quirks, and may even form physiologically in the form of ailments. These traumas can also lead to self-limiting beliefs in children that are demonstrated as they become an adult. Although recently there has been more emphasis on reaching out and getting assistance, this may limit a significant portion of the population, such as people suffering from self-limiting beliefs from trauma who may struggle with taking any steps to reach out for help. A response to trauma is avoidance, the unwillingness or fear of confronting their demons and this may lead to a person either running away from their problems, or not having the capacity to self-reflect and understand how their past traumatic experiences affect their behaviour. This inability results in the person not being able to challenge their belief system, leading the childhood trauma to continue its manifestation.