There are three main things that can interfere with the manifestation of our intentions. The first is the "yet" factor, which calls on us to remember that just because something hasn't manifested yet doesn't mean that it's not going to manifest. The second is the Highest Good factor which asks us to understand that the Universe knows better for us than we know for ourselves. Sometimes it's just not in our Highest Good - or the Highest Good of others involved - for our intention to manifest at this time. And the third thing that can sabotage us is doubt.
There is a old story about the Knower and the Novice that best explains how to deal with our doubts. When the Novice makes an intention and then, soon after, is faced with doubt or resistance, he tends to buy into the doubts. These doubts can be thoughts coming from inside him that tell him that he can't have, or doesn't deserve, or can't afford whatever it is that he's intended to manifest. Similarly, these doubts can also come from his outside environment in the form of well meaning friends or business advisors who say that he couldn't possibly manifest his desires. As the Novice buys into the doubts, regardless of their source, he sabotages his experience, loses trust in the Laws of Manifestation, and stops his forward movement.
The Knower is a different story. When the Knower is confronted with doubts or resistances, instead of believing in them, he ignores them and continues moving forward. He understands that the Intention Process always works - that we are all grand Creators, capable of great things - and all we have to do is trust that when we hold onto a thought that it will manifest for us. We may not know when or where. We just know that it will.
The Intenders of the Highest Good