Sure: if one isn’t in the right frame of mind, identifying one’s most inherent tendencies might lower in accuracy for some. However, Neuroticism (Big Five) positively relates to mental illness (on the high end: family dissatisfaction, abuse, lack of occupational commitment, antisocial behavior, etc.). There is extensive research on this… as well as Extraversion, Openness, Agreeableness and Conscientiousness being positively related to health, interpersonal relationships (not always for Openness, although there aren’t bad outcomes here either) and career performance success. One of the strongest personality papers indicates that these personality facets might be better predictors of life outcomes than SES and cognitive ability (although these are influential as well).