Virtually no great achievements occur without enthusiasm, frankly speaking to excel in life on a higher level you must possess it. Think about this, do you think a salesperson can close a big deal, an can actor give a performance of a lifetime, an athlete endure, through a sore body and run down the field to score a winning touchdown, a parent come home, after a long week and delightfully pick up their child, fly them through the air making buzzing airplane sounds as they dip and weave through the house WITHOUT enthusiasm? NOPE, it's not going to happen.
Enthusiasm is like life juice, it is a creative force that enables us as human beings to deliver excellence even when we are facing great obstacles. Enthusiasm lights a path wherever it has been and sets things ablaze, if you happen to be in its path, you know how infectious it can be and how it can almost instantaneously change your outlook or disposition.