The widely misunderstood common interest doctrine occasionally allows separately represented clients to avoid the normal disastrous waiver implications of sharing privileged communications. Among other requirements, most courts demand that the common interest participants share an identical legal interest. For example, a recent Privilege Point described a court's rejection of the common interest doctrine's applicability to communications between a college student and her mother – finding that the mother had no "legal interest in the case whatsoever" in her daughter's lawsuit against a college. Pogorzelska v. VanderCook Coll. of Music, No. 19 C 5683, 2021 U.S. Dist. LEXIS 120958, at *5 (N.D. Ill. June 29, 2021).

In Diamond Services Management Co. v. C&C Jewelry Manufacturing, Inc., the court applied the standard narrow common interest doctrine protection – requiring that the participants share "an identical legal interest, as opposed to a business or rooting interest" Case No. 19 C 7675, 2021 U.S. Dist. LEXIS 236193, at *11 (N.D. Ill. Dec. 9, 2021) (emphasis added). Fortunately for the participants, the court found the common interest doctrine applicable to some documents that had been shared.

The court's clever and useful term "rooting interest" helpfully warns lawyers that relying on the common interest doctrine requires more than sharing other participants' hope of legal success.