Final answer:
Augustus's original costume was the toga, and he ended up wearing a different one due to his belief that a change of clothing should align with custom and nature.
Step-by-step explanation:
Augustus's original costume was the toga, a traditional Roman garment. He wanted to revive the old style of dress and mandated that the toga be worn in the assembly. However, he ended up wearing a different costume because he believed that a change of clothing was only acceptable if it aligned with custom and nature. He considered his change of clothing to be a fault and a breach of nature, and therefore he reverted back to wearing traditional Roman attire.