Why does cecily mean when she describes her uncle jack ad being very serious?

Dear Uncle Jack is so very serious! Sometimes he is so serious that I think he cannot be quite well.

From the on top of the statement, taken from the text, it clearly tells Cecily's read regarding uncle Jack. She thinks that uncle Jack does not joke or crack a smile. She thinks he's thus serious that he can be unwell.

cassius, casca, and their allies plant false documents to manipulate brutus to join their cause to remove caesar. after doing so, they visit brutus at night in his home to persuade him of their views. there they plan caesar's death. brutus is troubled but refuses to confide in his devoted wife, portia. on 15 march, caesar's wife, calpurnia, urges him not to go to the senate. she has had visionary dreams and fears the portents of the overnight storms.

the objective should be switched