In any profession, you have to be extremely confident in your skills. I think if he constructively stated those facts, I would be 100% percent on his side regarding his platform about being a reserve (coming off the bench).
However, when the reporter asked about his "reserve" role against the Sixers, he said, "no comment". When asked about the Celtics' history of the "6th" man, he said, "no comment".
He sounds selfish because the team is having success. In fact, he didn't even play in most of their wins. How many championships has Marcus Morris won? Furthermore, how many winning teams has he played on during his career? I like him as a NBA athlete, and think he can really help this team. However, I'm concerned about this "me" attitude. Hopefully his comments won't affect coach Stevens' decision to start Baynes or Theis. The teams just plays better when the latter players play more significant minutes.