Depression and bipolar disorder, while they may share depressive episodes, are fundamentally different in their psychological dynamics. Depression is characterized by persistent sadness, hopelessness, and a disinterest in life's activities. Bipolar disorder, on the other hand, is characterized by not only depressive symptoms but also alternating periods of mania or hypomania, which include high moods, increased energy, and sometimes reckless behaviors. This cyclical nature of extreme mood variations is what primarily sets bipolar disorder apart from depression.