A generation reacts to the historical events that occur during its formative years. Their response to these events creates generational characteristics that stay with that generation throughout its lifespan.
For example, the G.I. Generation suffered through the Great Depression, and this generation tends to be quite thrifty.
Baby Boomers rebelled against the Viet Nam War, and throughout their lives, they have questioned authority.
The process of how generational characteristics are created is summed up quite nicely in the movie “The Iron Lady” by Margaret Thatcher:
Watch your thoughts, for they become words.
Watch your words, for they become actions.
And, watch you actions, for they become habits.
Watch your habits, for they become your character.
Watch your character, for it becomes your destiny.
What we think, we become.