The diathesis model explains that those who are already genetically predisposed towards a particular disorder, are more likely to show abnormal behaviour if exposed to environmental stress.
The disorder is a result of both biological factors (nature) and life experiences (nurture).
Stressful environmental experiences could be childhood abuse, family conflict, divorce, or death.
The model states that the stronger the diathesis, the lesser is the less stress required to trigger abnormal behaviour.
Hence, a similar situation leads to different reactions by different people.