The voice was passivized by the author
I just saw the following line in an ad:
I can’t believe it was made by myself!
…Certainly passive voice is not the only problem with that sentence. For example, the last word should be me rather than myself; a lot of English speakers incorrectly use myself to sound more formal or official in contexts where me is grammatically correct.
And certainly passive voice is not always bad. (Passive voice is a big complicated topic, with a lot more nuance than teachers and grammar reference works usually allot to it, and I’m not going to go into it in detail here.)
But even so, I was amused.