We know, for example, that during the 20th century there were terrible examples of mob psychology in which people were influenced by the groups of which they were members to think and act in certain ways. People do not construct reality. The Lord God Who made the heavens and earth is the One Who constructs reality. The episode of Jesus and the paralytic teaches us to cling to the Divine construction of reality as our Lord expresses it in His forgiving Word. In the same way, when Jesus a few moments earlier had said the man's sins were forgiven, those sins really were forgiven.
Forgiveness is invisible, but real.
Christ gave the Word, and it was so. As with the man's walking, Christ's forgiveness had no cause or basis in the man himself. God held Him responsible for the total sin of the entire human race. That was no fiction. It was real.