The study of the weak-ties phenomenon has a long and well-documented history, the research into the application of this social phenomenon has recently attracted increasing attention. However, a further exploration of the reasons behind the weak-ties phenomenon is still challenging. Fortunately, data-driven network science provides a novel way with substantial explanatory power to analyze the causal mechanism behind social phenomena. Inspired by this perspective, we propose an approach to further explore the driving factors behind the temporal weak-ties phenomenon. We find that the obvious intuition underlying the weak-ties phenomenon is incorrect, and often large numbers of unknown mutual friends associated with these weak ties is one of the key reasons for the emergence of the weak-ties phenomenon. In particular, scientific collaborators with weak ties prefer to be involved in direct collaboration rather than share ideas with mutual colleagues - there is a natural tendency to collapse short strong chains of connection.