The Norns are amongst the most powerful and mysterious beings known in the cosmos, and in fact they are not even unique to the Norse pantheon, as an identical triad of sisters are extant in the Greek pantheon, where they are known as the Fates. The Norns and the Fates may very well be the same beings, with power that extends over all pantheons and all sentient beings anywhere in the universe. Though the Norns are described in the myths as the three goddesses of destiny, it's quite clear they are not so much deities as personifications of the universal force of Fate, Destiny, or Kismet (take your pick of terminology), with each of the sisters representing a different aspect of time as mortals experience it in seemingly linear fashion--Urd represents the past, Verdnadi represents the present along with destiny in general, and Skuld represents the future. They are visualized by both the Norse and the Greeks in the form of three enigmatic sisters of variant ages (sometimes, but not always, as elderly) who are garbed in hooded robes. They are said to weave the tapestry of destiny for all sentient beings in the cosmos, including the deities themselves, which is why even the most powerful of the Asgardians respects their power and scope of influence. Though predestination is unknown to the Norse, and free will is believed to predominate our sphere of existence, certain events can be foredestined, but the individual decisions made by various beings during the course of their lives will determine to what degree--if any--these events will be actualized on any given timeline. Despite the existence of free will, the Norns nevertheless possess the power to greatly influence the course of events and to insure a beneficial outcome for the universe in general in most cases. They are said to often congregate before the Well of Urd (I am not sure why this celestial well was named after this particular sister), located in some far distant reaches of Asgard, but more likely in some realm that is accessible from but not actually within any of the Nine Worlds of Norse cosmology, since these beings could interact with deities of other pantheons who resided in otherworldly realms that were entirely outside of the Nine Worlds (such as Olympus, where the Greek deities live). It would appear that wells were for some reason archetypal symbols of areas where great knowledge or forces of various sorts could be accessed (note the Well of Mimir, also). This is possibly related to the fact that wells played such an important role in the material realm of humanity in ages past, since they provided life-sustaining water to those who lived in these agrarian societies of previous eras.
Forces of the universe have always been a major part of the mythos of various faith systems, and polytheistic faiths have often perceived them as able to manifest as sentient beings who are interpreted by mortals to be particularly powerful and mysterious deities. Even the proper deities give reverence to these great forces, because though some of the gods and goddesses are able to tap into and control these forces to a great extent, they nevertheless remain subject to their universal influence just as their mere mortal followers are. This is implicit in the story of Ragnarok, as Odin went to great lengths to try and prevent this destined cataclysm that would destroy all the Nine Worlds of Norse cosmology, but according to the myths he was ultimately helpless to prevent it. This would appear to make it clear that even the most powerful of the deities must to some degree bow to the great Universal Forces (which includes Fate/Destiny/Kismet, Death, Eternity, Order, Chaos), or at the very least being required to work with these forces rather than rising above them entirely. For this reason, I fear the Norns and the force of the universe they represent more than any single deity (including Odin, Loki, and Hela), and I often feel helpless beneath their irresistible metaphorical heel. However, I am also well aware that free will is another powerful force in the universe to be reckoned with, and I realize that I can affect the world I live in by the wisest possible decisions that I make, as well as by calling upon various of the deities, along with the Norns themselves, to do my best to control my destiny and forge it into something positive for both myself and for the greater good.