sentences:  In light of Wilson's increasingly fragile mental state, the group tensions, and his signing to Warner Bros., Parks's involvement in "Smile" effectively ceased on April 14, 1967, when he left to begin work on his solo career.Giving his reasons, he said, "I walked away from the situation as soon as I realized that I was causing friction between him and his other group members, and I didn't want to be the person to do that.I thought that was Brian's responsibility to bring definition to his own life.