In any legal malpractice suit, the plaintiff usually has the burden of establishing each of the essential elements, including proximate cause. Clients alleging that their attorney was negligent in connection with litigation have the burden of proving that damages resulted, as a result of the attorney's negligent investigation. Also, it has to be proved that the lawyer’s advice or conduct was a substantial factor in causing an unfavorable result.

Proof that the client would have prevailed or achieved a better result in the underlying lawsuit generally requires trial of a "suit within a suit". In other words, the law requires a determination of the merits of the underlying case in the malpractice trial.

However, there now appears to be a shift in policy. In negligence and products liability cases, for example, the law has evolved that the burden of proof may be shifted to the defendant. This also applies to situations when there is a substantial probability that a defendant's negligence makes it impossible, as a practical matter, for plaintiff to prove "proximate causation" conclusively. It is more appropriate to hold the defendant liable than to deny an innocent claimant damages.

This recent change in policy could be due to a number of reasons. One reason could be that the burden of proving an element is more appropriately borne by the party with a greater access to information. The defendant undoubtedly has more knowledge and professional expertise. Hence he or she should not profit from the claimant’s inability to produce evidence.