Judicial estoppel provides litigants with a useful tool to prevent their opponent from taking contradictory positions for tactical advantage. Once a party successfully asserts a factual or legal position, it is “stuck” with it and may not take a contrary position in a later proceeding simply because it would be advantageous to do so.
For example, in Otis v. Arbella Mut. Ins. Co., 443 Mass. 634, 639–640 (2005), the Supreme Judicial Court affirmed a trial court’s use of judicial estoppel to prevent a pedestrian hit by a car from taking a position in his action against the driver’s insurer which was exactly the opposite of the position he took in his claim against the driver. In his action against the driver, Cusick, the pedestrian, Otis, “took the position that he [Otis] was not negligent, based on the factual assertion that he had yielded the right of way when he … stopped a few feet shy of the dividing center line of the highway. That position was successful, as the jury found no comparative negligence on Otis’s part, and thus awarded him the full amount of damages for his injuries.” Later, in his action as Cusick’s assignee against Cusick’s insurance company, Otis contended “not only that he [Otis] was negligent, but that his negligence was even greater than Cusick’s, such that it should have operated to deny him any recovery against Cusick.” The SJC concluded that judicial estoppel properly applied because “[t]he factual premise now advanced in support of that comparative negligence theory is directly contrary to the facts Otis put forward in the prior suit—Otis now contends that he … had crossed several feet over the dividing center line and stopped in the direct path of an oncoming vehicle.”
“Judicial estoppel is an equitable doctrine that precludes a party from asserting a position in one legal proceeding that is contrary to a position it had previously asserted in another proceeding.” “In some instances, judicial estoppel is appropriate where litigants have asserted inconsistent positions in successive stages of the same litigation.”
“The purpose of the doctrine is to prevent the manipulation of the judicial process by litigants.” Judicial estoppel, “is properly invoked whenever a party is seeking to use the judicial process in an inconsistent way that courts should not tolerate.” The doctrine also protects public confidence in the courts. “Allowing a party to seek advantage from taking, “mutually exclusive” positions in different court proceedings would create[ ] the appearance that either the first court has been misled or the second court will be misled, thus raising the specter of inconsistent determinations and endangering the integrity of the judicial process.”
“Judicial estoppel ‘is an equitable doctrine, calling for the exercise of discretion in its application to particular facts.’” As such, the Massachusetts courts have made clear that “[J]udicial estoppel is not to be defined with reference to ‘inflexible prerequisites or an exhaustive formula for determining [its] applicability’” and that “the application of judicial estoppel must be decided on a case-by-case basis.” Whether to apply judicial estoppel is a matter within the trial court’s discretion. According to the Otis Court,
Like other courts that have grappled with the “hazy” contours of the doctrine, we decline to construct a categorical list of requirements or to delineate each and every possible exception. Rather, judges should use their discretion, and their weighing of the equities, and apply judicial estoppel where appropriate to serve its over-all purpose. That purpose is to safeguard the integrity of the courts by preventing parties from improperly manipulating the machinery of the judicial system, and judicial estoppel may therefore be applied when a litigant is playing fast and loose with the courts.
“The application of judicial estoppel requires both that ‘the position being asserted … [is] directly contrary to the position previously asserted,’ and that ‘the party must have succeeded in convincing the court to accept its prior position.’” The inconsistent position may be either factual or legal. Positions which are “directly inconsistent” are those which are “mutually exclusive.”
Even when a party has taken inconsistent positions, the court may, in its discretion, decline to apply judicial estoppel. The Supreme Judicial Court has noted that because judicial estoppel is an equitable doctrine,
there may arise certain instances where the party’s prior position was asserted in good faith, and where the circumstances provide a legitimate reason—other than sheer tactical gain—for the subsequent change in that party’s position. For example, “it may be appropriate to resist application of judicial estoppel ‘when a party’s prior position was based on inadvertence or mistake,’ ” New Hampshire v. Maine, supra at 753, 121 S.Ct. 1808, quoting John S. Clark Co. v. Faggert & Frieden, P.C., 65 F.3d 26, 29 (4th Cir.1995), or where “the position adopted in the first suit was clearly wrong yet had been advanced in good faith by the party now sought to be estopped,” Chaveriat v. Williams Pipe Line Co., 11 F.3d 1420, 1428 (7th Cir.1993). Strict application of the doctrine might not be called for if “the new, inconsistent position is the product of information neither known nor readily available to [the party] at the time the initial position was taken.” Alternative Sys. Concepts, Inc. v. Synopsys, Inc., supra at 35. Again, judicial estoppel is an equitable doctrine, calling for the exercise of discretion in its application to particular facts.
Although the doctrine of judicial estoppel applies only when necessary to prevent inequitable manipulation of the judicial process which undermines confidence in the courts, it is a powerful tool to force litigants to remain consistent in their factual and legal positions.
 Otis, 443 Mass. at 642-43.
 Id. at 643.
 Sandman v. McGrath, 78 Mass. App. Ct. 800, 801 (2011), quoting Otis, 443 Mass. at 639–640, quoting from Blanchette v. School Comm. of Westwood, 427 Mass. 176, 184 (1998). See also Turnpike Commercial Real Estate, Inc. v. B.C. Executive Realty, Inc., 92 Mass. app. Ct. 1130, 2018 WL 1145714, *2 (3/5/18) (unpublished Rule 1:28 decision).
 Turnpike, 2018 WL 1145714, *2.
 Commonwealth v. Middlemiss, 465 Mass. 627, 637 (2017). See also Sandman, 78 Mass. App. Ct. at 801, quoting Otis, 443 Mass at 640.
 Middlemiss, 465 Mass. at 637; Otis, 443 Mass. at 640.
 Otis, 443 Mass. at 639, 643. (Internal quotation marks omitted).
 Sandman, 78 Mass. App. Ct. at 802, quoting Otis, 443 Mass. at 642.
 Middlemiss, 465 Mass. at 637; Otis, 443 Mass. at 640
 Sandman, 78 Mass. App. Ct. at 802.
 Otis, 443 Mass. at 642.
 443 Mass. at 642.
 Sandman, 78 Mass. App. Ct. at 801-02, quoting Otis, 443 Mass. at 640–641.
 Faigin v. Kelly, 184 F.3d 67, 82 (1st Cir. 1999).
 Bay State Gas Co. v. Dept. of Public Utilities, 459 Mass. 807, 818 (2011); Johenning v. Town of Milton, 92 Mass. App. Ct. 1102, 2017 WL 3371725, *6 (8/7/17) (unpublished Rule 1:28 decision).
 Id. at 642. See also Holland v. Kantrovitz & Kantrovitz, LLP, 92 Mass. App. Ct. 66, 74 (2017).