1) Smarts and IQ don’t matter as much as everyone thinks and works hard for his goals. 2) Be optimistic in general but prepare for the worst. Your papers will get rejected, your advisor might change your project after you have spent several months on it, you may have financial or health troubles etc. Can you, in all this chaos, remain somewhat calm and get stuff done? That is what counts. 3) Self-care is cool. Can you take care of yourself? Can you take care of your physical and mental health, force yourself to exercise regularly, eat healthy food and have a social life out of the lab? When you are starting your PhD., these things may seem trivial. But, believe me, you will burn out and given the prevalence of mental health issues in academia, it will get to you. 4) The value of a PhD comes from the learning. Your PhD degree is not worth much if you did not learn the trappings of your field AND scientific publishing. Throughout your PhD, you should be learning new things (and getting papers outta them).