<p>Entrepreneurship requires the ability to deal with unforeseen events. New technology-based companies, called startups, undergo changes and adaptations to create innovative business models in environments of extreme uncertainty. According to the effectuation theory, entrepreneurs should take advantage of the available resources, determining a reasonable limit for the losses they are willing to face. Although effectuation theory has been widely studied, little research has explored how entrepreneurs use their resources and apply the theory to relationships to build their businesses in the face of unexpected events, especially in emerging economies, such as Brazil, with unpredictable environments and limited resources. The main objective of our research is to identify whether entrepreneurs, when dealing with various unexpected events, utilize the effectuation theory in creating their business models in highly uncertain environments. The methodology applied was the collection of semi-structured interviews with 18 Brazilian startups using the content analysis technique. The results allow us to infer that the entrepreneurs successfully create new businesses using their existing resources, adjusting the business model, forming strategic alliances, and anticipating contingencies in an unstable environment. However, when starting the growth cycle, entrepreneurs may make a decision that causes them to close down the new venture or decide to make a strategic exit. Thus, the article’s main contribution is to study the application of the effectuation theory in a local context such as Brazil. As a social contribution, this study is relevant to promoting entrepreneurial activity since understanding how entrepreneurs dealt with obstacles and seized opportunities can provide helpful guidance and inspiration for future entrepreneurs who wish to follow a similar path of entrepreneurial achievement.</p>