Mark 2:10 is the first place in Mark where the phrase "son of man" appears. Jesus is at the synagogue in Capernaum, where he sees a paralyzed man and tells him his sins are forgiven. The scribes think this is blasphemous. Jesus tell them:
'But that you may know that the Son of Man has authority on earth to forgive sins”—he said to the paralytic— “I tell you, arise, take up your mat, and go to your house.”'
Jesus spoke Aramaic, in which, if I'm understanding correctly, there is no audible difference between "son of man" (the idiom for any male human being) and the possible use of the phrase as a title, "the Son of Man." Therefore it seems likely that the scribes would have understood Jesus to mean it in the generic sense, as in Psalms 8:4, "What is the son of man, that you care for him? For you have made him a little lower than the angels, and crowned him with glory and honor. You make him ruler over the works of your hands."
Now the fact that the evangelist renders Jesus's snappy comeback in Greek as ο υιος του ανθρώπου, with "ο," means that he considers it there to be a title and a reference to Daniel 7:13. But from the point of view of the people Jesus is addressing, is it reasonable to construe the saying like this?
But that you may know that any man has authority on earth to forgive sins...
In other words, Jesus is simply saying that people can forgive people, and no special authority is required.