Your growth mindset, or lack thereof, is critically important to achieving or not achieving goals. There is nothing wrong with realistic optimism. And don't let someone tell you otherwise.
Over my career, I've witnessed those with growth mindsets are realistically optimistic and achieve their professional and personal goals consistently.
They have ability to work through adversity. They realize by working smart, hard, together, with focus and doing so with consistency, they will achieve their goals.
They don't get too high or too low. They are team players and give recognition to others. They are coachable and often seek out coaching. They realize they themselves don't have all the answers. They most often are self and situationally aware; and bring positive energy to situations, even challenging situations. They might fail, but they learn, and consequently grow and achieve goals.
Conversely, I've also observed those who lack a growth mindset. They might take convenient accountability in positive situations; but lack accountability/responsibility in challenging situations.
They often bring negative energy to situations. They themselves don't admit fault or failure....In their mind "someone else fails them and causes them to not achieve their goals". They often are inconsistent in achieving goals.