Many expected the reforms to fail, but the reverse proved true - they were a resounding success.

the 是定冠词，在这里特指"与预期相反的情况"。 reverse 作为名词时意思是"相反、反面"，来自拉丁语 reversus（转回）。这里指"与预期完全相反的结果"。 the reverse 这个短语表示"相反的情况"，强调与之前提到的预期形成鲜明对比。