The formation of Malaysia is one of the more significant episodes in understanding the country's historical chronology. This is because it symbolizes a large union in Southeast Asia through the merging of Malaya, Sabah, Sarawak, and Singapore. Behind the proposal for Malaysia's formation, there were various reactions both opposing and supporting among the leaders and people of Sarawak. The proposal surprised them because the purpose of this plan was unclear. Therefore, this idea initially received negative reactions from Sarawak leaders. The opposition from the leaders of Sarawak were clearly plastered all over the front pages of newspapers in Sarawak, Singapore, and Malaya. In response, leaders from Malaya, Singapore, and Britain endeavoured to persuade the leaders and people of Sarawak about the benefits of the Malaysia formation plan. This brought relief to most Sarawak leaders who desired independence along with development for Sarawak. Against this background, this article attempts to uncover the reasons why there was a shift from negative to positive reactions among a significant number of Sarawak leaders. To obtain the research findings in this article, the research method used is content analysis, utilizing primary materials from archival documents. Newspapers were also utilized in the analysis of this article. These primary sources are supplemented with secondary sources that provide a comprehensive analysis to address the questions raised in the article. In this regard, several books related to the history of Malaysia's formation are used. Findings from this study indicate that perceived assurances were sufficient for Sarawak's independence within the formation of Malaysia. This is the hope of leaders and people of Sarawak for joining in the formation of Malaysia.