Non-joinder of a necessary party means a key person whose rights will be directly affected by the result of the case has not been made a party, and without that person the court cannot pass a complete or effective decree. To deal with such situations, lawyers first identify all stakeholders whose presence is essential, then ensure they are added as parties at the time of drafting the plaint or written statement, and if someone is missed, they file an application to implead that person (for example, under Order I Rule 10 CPC in India) as soon as the defect is noticed, before the matter proceeds too far. Best practice followed by expert lawyers is to treat party-identification as a strategic exercise at the very beginning: map the legal relationships, avoid both non-joinder and mis-joinder, raise or cure objections early, and thereby protect the case from being dismissed or delayed on technical grounds instead of being decided on merits.