Why is it that people always say “When one door closes, another opens.”?

Personally I feel as if when one door closes its like a chain reaction. That first door triggers the rest to spring shut. One second you can be standing at the top of the mountain, and your life is exactly how it should be, then all of a sudden you find yourself in the mud. Where were the doors to save you when you were plummeting from euphoria? Of course after this happens the doors start opening again, but isnt it a little late?