I believe that we can do both, and that the question opens two deeper issues: How d we know which dreams are really ours? and, how do we relate to fear?
All the answers I see here seem to reflect these issues.
I discover my dreams and work to make them real, and encourage everyone else to do the same. But many people follow a dream - a particular career, or the pursuit of a particular success, or even service work - that is not truly their own dream. Let us each look deeply and find out why we are here, what combination of creativity and service and adventure and success is our truest dream.
With regard to being reasonable, if that means not harming ourselves or others, then that is great. But if being reasonable means being afraid to take risks due to fear of failure, then we fail by not putting forth our best effort.
So, let us discover our true dreams, acknowledge our fear, and step into action with courage.