Can you feel sure that something is true and doing so makes it true? That is, could belief become reality simply because you choose to make it so?

This is probably a stretch.  Making the impossible become possible is not a magical activity that is accomplished by a sweep of the wand.  However, attempting to elicit a change without believing it possible reduces the chance of success.

Trust in Yourself

Being sure something is true arises from a firm belief in your own judgment.  How you view your own reliability governs the strength of your belief and the intrinsic power of it.

Proceeding on the basis of blind faith can be risky and trusting in yourself without paying attention to reality could not only fail but also lead to negative consequences.

Self Doubt

It does make sense to temper your self-trust with a dose of doubt and some cynicism.   The trick is not to let self-doubt become the overriding factor in your decisions.

Doubt should be based on objective analysis to the greatest extent possible.  That is, where it makes sense to question whether something is true or whether you are able to make it true, this is best based on the supposition that is supported by some facts.

Accent the Positive

Having a strong belief and letting that drive your outcomes is really just a way to accent the positive.  Focus on the positive is far more likely to drive achievement of what you seek.

And for those that were wondering, this message of positivity is not brought to you by fox news.