I had a math teacher who claimed the opposite anecdote: he found that kids can do equations when there is x (obviously ones who are past their algebra fear): x + 5 = 10 is no problem. But then when you use some unfamiliar symbol, they freeze: △ + 5 = 10.

At that level, people tend to resemble trained models. I was trained on x, so I don't get it any other way.