Combat veterans are shown to be wiser for it.

Stress, even extremely traumatic stress, may pose both risks and benefits. Although combat can have lifelong negative consequences, the perception of positive benefits from military experience can mitigate the negative effects of combat on mental health. However, little research has examined the impact of trauma earlier in life on the development of positive adaptation, such as wisdom, later in life. The authors examined whether combat exposure and the perception of benefits from military experience, assessed in 1990, were associated with greater wisdom in later life, assessed in 2001 in 615 men from the Normative Aging Study men (mean age 74 years, SD = 6.8 years). A quadrilinear relationship between combat exposure and wisdom was found. Moderate levels of combat were associated with higher levels of wisdom. The perception of benefits and coping predicted wisdom. Thus, how one appraises and copes with problems may be more important in the prediction of positive adaptation than the simple occurrence of stress.
http://roa.sagepub.com/cgi/content/abstract/28/1/115