Thou shalt not block
In a game, everybody (PC or NPC) is trying to do things. Iinvariably they will come into conflict. As a PC you will encounter situations in which somebody is trying to achieve something, and you want it not to happen.
I want to be absolutely clear: I have no objection to your assuring that your enemies do not succeed at what they attempt. But I do have very fierce objections when you carefully arrange matters so that they may not even attempt it. Trying and failing is dramatic. Never trying at all isn't. Taking a dramatic possibility and making it flatly impossible is like erasing good drama before it can even happen. It is a sin, and it is called blocking.
The other, even more pernicious, form of blocking is to try to erase good drama after it has happened. Suppose your character defended a shadow-town from monsters, but in the process she failed to defend one of the townsfolk, the mother of a small child. Now the child is orphaned and miserable... drama. She could adopt them as a squire, or scorn them at the risk of their growing up bent on vengeance, or find them a family and check up on them from time to time. All of these are good for the story.
But with the power of a Princess of Amber it can be very tempting to conjure up a shadow of the dead mother from somewhere she wouldn't be missed, in order to put things back exactly as they were. This isn't reacting to the consequences of the story, it is erasing them. Bad, very bad. Resist temptation!