13 And because of this their great wickedness, and their boastings in their own strength, they were left in their own strength; therefore they did not prosper
This is a powerful refrain in the Book of Mormon. When those who allege to be the people of God forget him and begin to rely on their own strength, they begin to falter. I think this is absolutely the case for each of us individually. This isn’t to say that neglecting God will instantly bring consequences of decay. Often, we can continue onward and even prosper for a time without him. 

But where it really counts, we are stymied without faith in God. Most significantly, our growth towards becoming like Christ is halted. We cannot become like him if he is far from our thoughts. We need his constant support in order to overcome the growth of the natural man. Without him, our vices will grow and our virtues diminish. We will become more and more fixated on worldly pleasures and less on the things of eternity. 

This process of forgetting God happens so gradually at times that we may not even notice it happening. But we need to be hyper vigilant to prevent it.