Life is fluid. Everything is constantly moving, changing, evolving because life involves a lot of people. Perhaps if you stood in isolation, dependent on no one else and having no interaction with anyone else, life might be predictable. However, your life involves a lot of different people who are independent in their decision making. Even you, with your many decisions in a day, cause life to be fluid. This is the reason we should never assume.
We are dependent on Yahweh, or at least, we are suppose to be. We are suppose to be in constant communication, checking his will and direction. He adjusts our actions according to the decisions of other people so that his will is always fulfilled. That means it is not one set of instructions and off we go. He goes with us for a reason, so adjustments can be made. This is why he desires obedience from his children, so we will listen constantly and obey in love and trust. We have an example of this with Joshua and the Israelite's.
They just had an awesome victory at Jericho. It was a bit odd but the purpose was to show them that Yahweh was giving them victory and it was not dependent on their army. He had given them exact, step by step directions. So now their sights were set on their next objective, the city of Ai. Joshua sent the spies and they came back with this report:
Do not let all the people go up, but let about two or three thousand men go up and attack Ai. Do not weary all the people there, for the people of Ai are few. (Joshua 7:3)
Confident on the heels of their victory, they did not consult with Yahweh. They assumed. But life is fluid. None of them could possibly have known that the situation had changed. One of their own had disobeyed Yahweh's instructions in the first battle and because of his sin, Yahweh had removed himself from Israel. When they went up to attack Ai, a much softer target than Jericho, they were thoroughly defeated and people died. People died, not just because of Achan's sin but because the leadership had failed to consult Yahweh. If they had verified things with him they would have discovered the change in their situation.
We can't make assumptions with Yahweh. We must remain in the Spirit, being sensitive to his voice so when adjustments need to be made we will be in the know. If we do not understand and practice the presence of our Lord then we will have the mentality of a commander receiving instructions from the general, then going out without the general to carry it out. Then again, a general always has contact with his troops in the field for the purpose of adjustments as the situation changes.
Practicing the presence of the Lord Jesus Christ is more than for our strength. We often get selfish in this relationship, thinking it is always about us. It is true that being aware of his presence is a great source of strength and confidence, but his presence is also for direction. You have never been left alone to do this on your own because on your own you are not capable. You are not capable of understanding all the changes in our fluid lives, but the Spirit is and he is here to direct us in our Father's will. So learn to listen and obey.