We have all heard this a million times before in a million different ways. The question is if we have heard it and we understand it as a concept why are we not living it. The answer to that is very simple FEAR (False Evidence Appearing as Real )
The fear is not because of not knowing even though that is a part of it it comes from not understanding for we fear what we do not understand however we can not understand unless we investigate which means we have to move outside of what is known. Once you investigate the unknown it becomes the known and comfort returns because you understand it is just that first step you have to take.
The Ego says what if it is worse what if we can't come back what if, what if, what if. You can always come back to an understanding it never leaves you once you have it it is yours, the spirit, on the other hand, plays what if as well what if this leads me to happiness what if this leads me to fulfillment what if, what if, what if? who do you want to play what-if with?