The webcomic with the rotating taglines.
The Copenhagen interpretation of quantum mechanics says, more or less, that every time a quantum event occurs - such as the decay or non-decay of a radioactive nucleus - the quantum wavefunction for the system goes on to exist in a superposition of states, in which the different outcomes are all potentially present, but not realised. The system remains in this ghostly mixture of states until some outside observer measures the system, at which point the wavefunction collapses into one of the possible states. Prior to this observation, the system cannot be said to be in either state. Since quantum events happen all the time, much of the universe can be said to exist in an indeterminate, mixed state, until you look at it.
Given this, every time you make an observation, you are collapsing the wavefunction of the universe from one in which all the possible outcomes are represented into a state where only the actual outcome occurs.
Unfortunately, these momentous events of wavefunction collapse 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 which button you observe yourself pressing, and therefore how you choose to collapse the universe's wavefunction. Choose wisely.