When Dream Grail was just a filly, she and her Pegasus friend went to a wonderbolts derby to see the races, and to make things even better, a contest was held that the winner of the lucky ticket will get a chance to fly with the wonderbolts for an hour and Dream Grail had the winning tickets, the problem was that Dream Grail couldn't fly due to being a earth pony, but instead of choosing a different pony (a Pegasus) one of the wonderbolts instead let Dream hop on his back and enjoy the ride. During the flight Dream saw the wonders of the sky then when the hour was up, the wonderbolt set her back down to her sit and flew back into the air as Dream was still happy for what she have seen.
That night while sleeping, Dream had a dream where she found herself in the sky but instead of falling she floating, just then she sees the wonderbolts flying past her as she began to chase after them, as she chase them high and low and even doing a few aerial flips, she then saw that she is wearing a wonderbolt uniform and she and the others flew to the sunset. The new morning As dream went downstairs to get breakfast, her family looked in awe as they see that she has gotten her cutie mark, which is a white cloud, which also confuse the family as they wondered what could that could mean for her talent and Dream thinks she knows what the cloud means.
A few days later while in school, during a oral report of "what is your dream?" Dream stand in front of the class and told them that her dream is to one day became the first earth pony in history to be a wonderbolt, however the class then laughed at her after hearing her dream, which cause her to got back to her sit feeling embarrass after saying that. Then during recess she cross path with a brother/sister Pegasus siblings who mock Dream's dream of being a wonderbolt as they said that only Pegasuses can be wonderbolts because they are flyers and she is just an earth pony but Dream said she going to make her dream come true no matter want. So while reading up with the ENTIRE history of the wonderbolts and their fly routes, she set out tp prove she can make her dream come true, no matter how much it will take and become the first earth pony to join the Wonderbolts.