Why is it the bigger life events seem to happen in clusters at a time?

It seems like life is cycles of working with day to day routines, than the bigger life events seem to happen in clusters like getting a new job, moving, birth of new family member, dating, weddings, loss exc. And of course they happen all in their own order it seems at times when life happens in multiple events at a time

Why is it the bigger life events seem to happen in clusters at a time?
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