It is known that people who do not handle changing life circumstances well might be particularly vulnerable to the slightest frustration or pressure.  Those who are generally unsure of their adequacy and worth are much more likely to experience threat than those who feel generally confident and secure.

When we refer to stress tolerance we are referring to a person's ability to withstand stress without becoming seriously impaired.  People are all different and vary greatly in overall vulnerability to stressors.  People who have a history of major depression are more likely to suffer serious psychological issues after experiencing stress from a trauma such as a car accident (Blanchard, Hickling, Taylor, and Loos 1995). 

Some people appear to be constitutionally more frail than others and tend to struggle with even relatively minor changes.  They do not have the physical stamina to cope with some of lifes demands at times and may become tired or sick when placed in stressful situations.  In addition to this, different people are vulnerable to different stressors and sometimes this is due to the experiences they have had so far in their life.

Our individual learning history plays a crucial part in our general capacity to deal with stress.  Early traumatic experiences can determine if we are going to be particularly vulnerable to certain stressors or perhaps even especially able to handle certain stressors.  A lot depends on how we coped with that traumatic experience at the time.  Some people are able to completely 'forget' or 'choose not to remember' specific events, child or sexual abuse is a common trauma that causes this type of amnesia.  While this denial appears to protect the person in the 'here and now' it may cause issues longer term.