Quitting a postdoc: how to justify myself with my PI? I am 8 months into a postdoc that  is not matching with the job description and the proposal. The project was about investigating an unknown phenomenon that emerged during some experiments carried out before my started.
However, someone just switched some columns in some databases and this caused the misinterpretation. Therefore, my project now only consists in fixing the databases, and what is emerging is that there is no new phenomenon at all. There is nothing new worth a publication.
Since I already have an alternative lined up, I will quit my present institution. I will give no more than a two-week notification before leaving, as I have to start with the new position.
Some other info:

my PI perfectly know of the situation and of the data mistake.

fixing the remaining data is something that someone else in the team could easily do and in any case it is so trivial that they will be able to find a replacement.

I do not have any teaching or mentoring assignments.


Now the question. What should I tell my PI? Should I be sincere and (politely) tell him that I don’t like the project anymore? Or should I find some other excuse not to risk offending him?
If he is a reasonable person then be honest. Something like:
I was happy and enthusiastic to come and work with you on the project, but it changed before I started and I don't see any advancement for me in the current situation. I've found another position that I think will be more productive and need to start it soon. I'm sorry that it didn't work out.
Hopefully all of that is true.