When I lived in Mexico I discovered that many of the assumptions I had were determined by my culture rather than by reality. For instance, I assumed that everyone knew there are seven continents on Earth. I didn't realize that something I considered "fact" could subtly color the way I perceived life until I encountered people who were taught there are 5 continents, or 6. Does Antarctica count when no one lives there and there are no political entities or cultures developed over generations? Are North and South America one group (New World) or two? What about Europe and Asia?
In the same way, we can assume things to be true which the Lord would say are not. We don't realize they could be different because everyone around us holds fast to those same beliefs. Yet as Christians when we immerse ourselves in God's word and allow Him to adjust our perceptions of reality, we discover that there is another way to look at the world. Our society may have taught us that the ultimate goal of life is our own happiness, while God teaches us to bring joy to others. The world may have promoted a definition of success which is very different to the Lord's definition. For every belief we hold we need to question, sometimes several times over the years, whether that belief is an assumption taught by the world we live in or is it a truth revealed by the Lord.