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The Copenhagen interpretation and the many-worlds interpretation of quantum mechanics are two different, consistent, but mutually exclusive interpretations of what happens during a quantum event - such as the decay or non-decay of a radioactive nucleus. In the former, the system exists in a mixed state of superposed wavefunctions until an observer looks at it, while in the latter, the universe splits into multiple universes in which the system exists in well-defined, but different states.
Given this, each time you make a decision (or an observation), you are deciding to choose whether to collapse a wavefunction or create new universes.
Unfortunately, these momentous events of quantum mechanics interpretation pass most of us by unnoticed. We all have superficially more important things on our mind most of the time. Which is a great shame.
So here is a decision for you to make which has no implications other than how you choose to interpret quantum mechanics. Choose wisely.