In some jurisdictions, the principle is strictly enforced to avoid any appearance of bias, even when there is none: as Lord Chief Justice Hewart laid down in Rex v. Sussex Justices, "Justice must not only be done, but must also be seen to be done".
In certain jurisdictions, the principle is rigorously applied to prevent any appearance of bias, even if there isn't one present: as Lord Chief Justice Hewart stated in the case of Rex v. Sussex Justices, "Justice should not only be carried out, but also appear to be done".