A man who is his own lawyer has a fool for a client
The Flowers of Wit, or a choice collection of bon mot By Henry Kett 1814.
In Duckworth -v- The State of Western Australia [No 4]  WASCA 2 Chief Justice Martin made the following comments about self-represented litigants and appeals in convictions relating to a trial conducted by self-represented litigants.
…[T]he principles… of deficient legal representation focus upon the question of whether the course of the trial involved a departure from fundamental notions of fairness, or a material irregularity productive of a miscarriage of justice.
The fact that an appellant represented himself or herself at trial, for reasons other than indigence, may be relevant to an assertion that the deficiency of representation resulted in a miscarriage of justice in at least three ways.
First, the standard of competence to be reasonably expected from a qualified legal practitioner will obviously differ from that reasonably expected of a self-represented accused who is not legally qualified.
Second, an accused person representing himself or herself at trial will not have the professional detachment of a legal practitioner who does not have a direct personal stake in the outcome of the trial.
Third, a self-represented accused might perceive a potential advantage in conducting the trial in such a way as to give rise to either a miscarriage which results in the trial being aborted or a good ground of appeal in the event of conviction.
… [T]he conduct of a self-represented litigant, although irregular, will not necessarily deprive the accused of a fair trial. Not every error makes the trial unfair.
A miscarriage of justice has two aspects, process and outcome.
The ultimate question of whether a miscarriage of justice has occurred raises two issues. First, did the self-represented litigant’s conduct result in a material irregularity in the, and secondly, is there a significant possibility that the irregularity affected the outcome.