This has happened to us as well, but for reading. Both my kids would do this but more so my daughter: they'd scan the first section of text they were about to read and if there was a name included that they'd never seen before they'd refuse to read. "I can't do it" or "it's too hard." I just figured it was perfectionism. It confused the heck out of me at first (as in, I knew they could read it) but once I figured out that the name was the issue I'd simply read it out loud myself first.