Sonny was not so much negligent as he was not thoughtful. As the novel points out, Sonny had a tactical skill that few exceeded, but he lacked the strategic ability of this father. Thus, he chose to use the approach with which he was most comfortable: warfare. He eschewed diplomacy because he did not know how to utilize it. Tom did. Sonny should have combined his tactical skill with Tom's diplomatic skill. To the extent that he didn't, he was negligent.