Excellent Science, Technology, Engineering, and Mathematics (STEM) employees are in constant demand worldwide. The current study explores Israeli students' choices to study and pursue careers in STEM fields, while students' level of excellence in mathematics in secondary school is explored as a predictor for choosing a STEM track in future study and employment, as well as a predictor for the level of success in completing a STEM degree. The theoretical framework for the study is based on the task performance model of the social cognitive career theory which focuses on human behavior in the context of career choice. The study presents a big data analysis based on about 650,000 records retrieved from the Central Bureau of Statistics in Israel for several points in time over the last one and a half decades, to demonstrate choice patterns over the years. We analyzed a representative sample using systematic sampling over the last decade and a half, from secondary school, higher education, and postgraduate STEM-related populations who are employed in STEM professions. Our study presents a scale for mathematics excellence, which reflects a combination of study level and level of success. Our findings reveal that choosing a more advanced level of mathematics in secondary school, as opposed to the level of success in these studies, is the best predictor for choosing STEM as a major in secondary school, completing a STEM bachelor's degree, succeeding in a STEM bachelor's degree, and making a STEM career choice.