Insurances form risk groups by gathering people who are susceptible to a common harm. They collect their funds by the payments of their clients, which have been assessed based on the law of large numbers, and guarantees coverage for the insureds’ loss by paying claims. When unanticipated accidents occur, the insured can treat their disease or compensate for their financial loss through the premium they receive from the insurer. As such, insurances enable individuals to pursue a secure life by allowing them to prepare for unexpected losses at a relatively low cost. Hence, they have become a crucial aspect of the modern life. However, individuals have begun to sign insurance contracts while lacking thorough explanations about their terms as they have become complicated, and special provisions have been included along with the diverse causes of diseases and accidents. As a result, legal disputes about refusal of insurance payment due to interpretation of clauses are continuously increasing. Especially, interpreting clauses of ‘hospitalization and surgery with the primary purpose of treatment.’ is becoming one of the most major issue in recent years. Considering the nature of insurance contracts and their clauses, it is extremely difficult for the insurer to explain every clause to the insured, nor it is essential for the insured to completely understand each clause. Nonetheless, decisions to sign a contract should be made after receiving a detailed explanation about the financial compensations the insured will receive for their loss, and fulling understanding the scope of its coverage, the major clauses, and the exclusions. However, such information is often left oblivious when signing the contract, and the information regarding ‘hospitalization and surgery with the primary purpose of treatment,’ which is the criterion in which insurance claims are inspected, is generally unmentioned nor explained to a degree in which the general public can understand. Therefore, it is common for the insured to be unable to receive any payment from their insurance, even when they have been treated for illnesses that were mentioned on their contract. Insurance companies argue that hospitalization and surgery do not have the primary purpose of treating the targeted disease, and that they are not obligated to explain the term, ‘hospitalization and surgery with the primary purpose of treatment.’ However, the duty of explanation should be judged from the perspective of the insured. Reflecting on the legal principle that any significant term, which has influence on the insureds’ interest, is liable for the duty of explanation, the scope of the ‘hospitalization and surgery with the primary purpose of treatment,’ and the fact that only claims that fall into its scope are covered should be considered as clauses that ought to be explained. Therefore, when a contract includes a clause about ‘hospitalization and surgery with the primary purpose of treatment, the insurer has the obligation to thoroughly explain it in comprehensible terms. Moreover, when such obligation is unfulfilled, the insurer cannot argue that the insured has consented to the contract. In addition, neither the insurance contract nor the related laws stipulate the scope of 'hospitalization and operation for direct treatment'. As a result, each level of courts has made different arbitrary judgement about whether or not to pay insurance payments, and individuals have suffered unexpected damage. Therefore, fundamental solution to prevent dispute about interpreting 'hospitalization and operation for direct treatment' is needed. In addition, to prevent dispute due to differences of interpretation of the terms and correcting the imbalance of information between insurer and policyholder, specify scope of "Hospitalization and Surgery with the Primary Purpose of Treatment" in the terms or insurance-related legislations may be an effective mean and be expected accomplish purpose of the insurance systems.