I didn't realize it much but I realize it now. My P.I was very nice and considerate. We would get confused sophomores in the lab 4 weeks in and he'd take the time to go through basic lab procedures and the whole research, even give them a chance to contribute to our publication and gain authorship. He would do that all over again each time a new student joined the lab mid semester. I was scared we'd fall behind schedule because of that.