There is a pivot point where Doctor Strange can either choose to use the Eye of Agamotto to go back in time and try to save Christine’s life — or, conversely, he can at least try to accept her death and move on with his life. The Ancient One (Tilda Swinton) splits Strange into two versions of himself because she foresees how Strange’s actions will bring about the death of reality, and the only person who can prevent these events is Steven Strange.
There’s one other being who foresees these cataclysmic events unfold before they happen: The Watcher. As the Dr. Strange who seeks the power to alter that which cannot be altered, he feels the presence of The Watcher. In a moment of empathy and even vulnerability, the Watcher contemplates stepping in to alter events before it’s too late. However, he lets events unfold because, according to the Watcher, to alter this timeline would mean risking other realities.
When Dr. Strange does bring Christine back, reality is destroyed. Strange calls out to the Watcher to change things, and the Watcher explains that he cannot because he is not a god. However, because of the scene he appears in earlier, we know that the Watcher could have changed things at one point, but chose not to.
We’ve long suspected that the Watcher chooses only to watch and we’ve also long guessed that, not unlike the TVA, there is at least one timeline which the Watcher values over certain others. The Watcher can interact with mere mortals and he can change things, but he hasn’t — at least not so far. With an MCU about to be rocked by the complexities of the multiverse, who knows if the Watcher will change tactics.