We always have a choice. We can always do the wrong thing, if we prefer. The right choice may be obvious, but we are under no compulsion to take it. After all, nothing is true, there is no rightist choice, only the best we current know. We are free to challenge any known truth, violate and test it, or ignore it completely. It is ultimately up to us.
And choose we must, for the world will not wait. Actions will come upon us. Decisions will need to be made. Life continues, the world continues to try to interact with us, and we cannot ignore it for ever. The world is real, and has to be dealt with in some manner, even if it is the choice to not deal with it at all. After all, we can choose this as well.
We are, but we can choose to no longer be. This is the most shining example of the power of choice. We can choose to ignore even the Foundations themselves. This is the power in the Self, of the Will. Suicide remains a possibility. Not a good one, granted, but because we can choose it, we know that we still have our will.
So, we decide to accept the foundations. For each, if we choose to refuse them, we can no longer go forward. After all, we can do this if we want, the Will will allow it, but we will go no further if we do. Therefore, we choose to accept each of the foundations: That nothing is ultimately true - thus insuring that we remain flexible to new possibilities, that the world and reality is real and to be dealt with - thus protecting against delusion and keeping us grounded, and that we exist - thus that we continue to play the game.
Violation of the foundations results in the end of the game. But there are other ideas which make up the basis of our belief that can be wrong, without a complete breakdown of ourselves. There are things we are less sure of, but we decide to accept them as true. We assume them to be true for the sake of argument, so that we can build upon them as well.
These assumptions are made knowingly, with open eyes and rational mind. We decide to make them true, knowing that they could be wrong. But it is important to us that they are true, for our own reasons. It is just important to remember always that we decided to assume them, that they might be proven untrue. If they are, we can choose to reject them and still have our foundations to fall back upon, to develop new assumptions, and continue to build our belief.