make a big mistake(According to grammarian Michael Swan, both "great" and "big" are acceptable, the difference being "big" an informal word.: You are making a great / big [informal] mistake.ART Vancouver)
make a great mistake(According to grammarian Michael Swan, both "great" and "big" are acceptable, the difference being "big" an informal word.: You are making a great / big [informal] mistake.ART Vancouver)