Start-up founders mainly proceed according to classic business management methods. Based on market research, product portfolios and analyses of strengths and weaknesses, business plans with planned strategic and operational goals are created and financial plans and milestones are drawn up. However, these have little in common with the later reality because start-ups operate in an uncertain environment with their innovations. They therefore have a high probability of entrepreneurial failure.Effectuation can help to reduce the risk of entrepreneurial failure by applying effectual principles. The book describes, among other things, which essential approaches of effectuation are helpful for start-ups and under which aspects effectual and causal methods have advantages. From the expert interviews conducted as part of a qualitative research process, recommendations for action were derived that can help future start-up founders to reduce the probability of failure.