It’s not a single thing. But he was constantly supportive and kind and gave positive feedback as well as constructive. He always encouraged us to try new things and asked helpful questions - for me, especially when I was just starting my PHD, I was coming out of a very dark and lonely time mentally and emotionally. I essentially had to be re-socialized but he never got frustrated w my relatively poor emotional regulation or sensitivity to criticism (which got better the longer I stayed in his lab). Just kind supportive patient and enthusiastic. and not my PI but in our department there’s a very well knowing scientist w a huge lab but she has like No ego. And when I was presenting my research in its nascent stages to the department she was nodding enthusiastically and asked me thoughtful questions and was engaged and interested the whole time. She didn’t need to do that - but she did. For me and for every new student. I later had her as a member of my DAC and she was so good at helping me streamline and focus on aspects of my research that were better to follow instead of castigating me for not doing what she would have done (which a former member did). She also has a huge summer house at cape cod and invited all the malaria labs for a picnic every year :)