why did taplow feel bitter

Mr. Crocker-Harris had called Taplow to the school as Taplow had missed a day of class last week because of illness. Taplow had thought that he wouldn't be called for to make up for the missed class because Mr. Crocker-Harris was leaving the school, however, it was not to be so. The strict teacher had called him even at the last day of school to tutor him in his Greek lesson. This made Taplow bitter. Further, he did not find literature much useful or interesting and was more inclined towards science, which is why he was more irritated on having to come for a lesson.