R’ Moshe Bogomilsky shlita (Vedibarta Bam) would say: “'וישמע ראובן ויצלהו מידם' - What did Reuven hear that made him decide to save Yosef from the hands of his brothers? Rashi says that Reuven heard his brothers say, ‘Let us kill him ...’ but this was actually Ruach Hakodesh - the Holy Spirit. Hashem was saying, ‘You are planning to kill him; we shall see what will be with his dreams. Will your plan be realized and he will be dead, or will My words be fulfilled and his dreams will come true?’ The brothers did not hear this Holy Spirit, but Reuven did. Thus, he immediately decided that he was obligated to save Yosef and bring him back to Yaakov.”
A Wise Man would say: “Knowledge is strength, but true wisdom is power.”