being proud vs being annoyed

Sometimes the impression I have of my students can change from one day to the other.

A few days ago I was quite proud (and relieved) because one of my students finally seemed to have grasped the concept that setting up your experiments properly right away might cost you more time before you can start your experiment. But having thought of all the tiny things that can influence your measurements and maybe having fixed a few issues might save you a lot of time in the long run. He learned that the hard way by being forced to re-do a bunch of his measurements because the original experimental procedure was too sloppy. Finally it seemed that he understood the concept and he even started searching for answers for some of the peculiarities in his data without being pushed by anyone.

Then he stumbled over a new issue just recently, which is based on sloppy sample preparation. I had told him already a year ago that he has to implement a special sample prep step to avoid this problem, but he did not believe me at that time and prepared the samples the way he thought was sufficient. So, now the bad sample prepping finally shows its full impact. And he says: "You certainly never told me about this!", AAARRGGSSSZZZLLLL... even if for some reason I would have kept this information from him, he should have been able to filter it out of the literature (that I guess he must have read by now) or even figure it out by just sitting down and switching on his science/engineering brain, because it is a very obvious an reasonable step that needs to be added. But just saying it's my fault? Will I get the PhD title for his work or will he?

So the "being proud" is gone on holidays and the "being annoyed" took its place!