Thoroughly investigate any human endeavor, and error can be found.  Legal malpractice law holds that one must demonstrate that "but for" the attorney’s error, there would have been a better or different result.  This case, Cohen v Weitzner ,2008 NY Slip Op 00618 ,Decided on January 31, 2008 .Appellate Division, First Department  illustrates the rule:

"Plaintiffs allege that the settlement required them to pay more in taxes than they had anticipated based on a spreadsheet prepared for them by defendants in which, due to a typographical error, their tax liability for the year 2000 was understated by $121,000, and that they have been damaged in that amount by defendants’ misrepresentation. However, plaintiffs’ tax liability was correctly reflected in the returns they filed before retaining defendants and entering into the settlement agreement. In any event, their tax liability was not the subject of the negotiations with the IRS. Thus, plaintiffs fail to allege how defendants’ error damaged them (see Lama Holding Co. v Smith Barney, 88 NY2d 413, 421-422 [1996]; Zarin v Reid & Priest, 184 AD2d 385, 386-387 [1992]). Further, as defendants were retained to try to obtain a reduction in the penalties assessed against plaintiffs, and they succeeded, there can be no claim
that they breached a duty to plaintiffs (see generally Dweck Law Firm v Mann, 283 AD2d 292, 293 [2001]). "