I once saw a reference letter that a Senior Physicist had written for a colleague I had worked with closely. The letter compared my colleague to me, along the lines of “X is as good as Jon at Y, but in addition is excellent at Z”.
I wasn’t best pleased by this.
X and I had worked as a team, and I felt it was quite clear that I brought Y to the table while X brought Z (hang in there on the variable substitution) and together we were a truly excellent team covering both Y and Z. Senior Physicist was talking out of their… ignorance.
Anyway, it’s not that I have brooded on this for ages (really I haven’t and both me and X are doing fine career-wise, thanks). But I do worry about references, especially now I am myself a moderately Senior Physicist so am asked to write them quite often. I was reminded of it by this good article from Tim Tait, in Physics Today, about the culture and comparisons of reference letter writing. If such things affect or interest you, I recommend it.