The situations and pressures that cause stress are known as stressors. We usually think of stressors as being negative, such as an exhausting work schedule or a rocky relationship. However, anything that puts high demands on you or forces you to adjust can be stressful. This includes positive events such as getting married, buying a house, going to college, or receiving a promotion.
Of course, not all stress is caused by external factors. Stress can also be self-generated, for example, when you worry excessively about something that may or may not happen, or have irrational, pessimistic thoughts about life.
What causes stress depends, at least in part, on your perception of it. Something thats stressful to you may not faze someone else; they may even enjoy it. For example, your morning commute may make you anxious and tense because you worry that traffic will make you late. Others, however, may find the trip relaxing because they allow more than enough time and enjoy listening to music while they drive.