doubt
If we don't occupy our mind, it will be occupied by things that are not us. In saying this, I extend that our foundations are either built by circumstance or by intention. When we are intent with our growth and our aspirations, we are able to be more consistent in our pursuit of that which we want. We must in this same way feed ourselves, in a mental sense, things that will allow us to grow in a good way. Our growth has always been characteristic of our ability to give ourselves what we need, and reject what we don't. When we vest ourselves in negativity, we cannot possibly think a positive version of ourselves will emerge. Doubt in this way, is having faith in a negative outcome or identification with issues, rather than solutions.
To say don't leave space for doubt, is to say that we need to learn to take up our own space. Sometimes we get so caught up within the idea of who we are that we fail to add more. Giving ourselves space, at least in mind, permits us to transcend what we have previously taught ourselves. A great deal of us have been conditioned to think negatively about who we are and what we do. If we aren't at the forefront of our own desires, we tend to fall into a process of self neglect. Not to say that our entire mind should be fixed on our own progression, but it should at the least have us within it.
The separation we create between who we are now, and who we will be in the future often creates our separation from our desires. We think that we are in a sense finite, not fit for what we wish to achieve to the extent of inaction. When we are unable to act, our goals become mere thoughts. We must in a real way, give ourselves a better opportunity to genuinely move towards our desires. I feel as though we have to have a large amount of faith in ourselves in order to do anything real. I think a certain amount of authenticity will allow you to be in the world, without forcing yourself to be a certain way.
The love we have for ourselves should be rooted in love, not in condition. We often place conditions on ourselves to do practically everything. “I need to be more confident before I… I need to work on myself before I can…” without recognizing that the work you need to do is always in the moment, not in the mind.

