In a story, fate is a factor that determines the direction of every single action that every single character does. That is because fate shapes the general plot of the story. In order to fulfill a fate, everything needs to fit perfectly with everything. The most basic way for doing that is to limit the characters' doings with a certain "range of action." For example, the gods and goddesses in the book are not able to alter the fate. Even though it may be because of the general academic definition of fate, in which I have stated in 1.1, gods have enough ability to change almost everything in the world. Also, although Aeneas meets many temptations, such as love, he manages to survive through them.
By researching, I have found out that almost all fates only control the outcome, not the process. This also applies in the Aeneid as well. As I have already mentioned in 1.2, Juno clearly knows that destiny has already determined the success of Aeneas, but she also knows that destiny cannot stipulate the "how" of the voyage. Juno uses that as her angle to give the Trojans an incredible amount of trouble. The result of the fate, as you know, is the founding of Rome, but it cannot be directly fulfilled by Aeneas himself, but his future descendants that were mentioned quite a few times in the story. For example, on Aeneas' shield and in the Underworld the successful future of Rome can be seen.