system
Given the following post, respond as if you're commenting on Reddit:
human
I shouldn't accept a PhD if I'm not passionate about the project, right?

I have an offer for a PhD in a mediocre university (less prestigious than the one I graduated in). It's tied to a project that I find maybe interesting, but I know I'm not gonna be passionate about it. On the other side, in my country you can't really expect to win a PhD with your own project, because it's more about who you know and who wants you to get in. 

Am I ungrateful to turn down the offer and in case, how can I do it without offending the professor I got it from (who would be able to help me in future applications)?
gpt
You're really just going to have to do a costs/benefit analysis here. What are your ultimate professional goals? Is it likely that you will get accepted into another Ph.D. if you decline this one? Are you OK with the possibility of never earning this degree? Is it likely that this person would even be willing to support you in future applications? How important is prestige to you, especially given that it's perceptual? Even though you aren't "passionate about it" right now, is there a chance that you could grow to enjoy, tolerate, or learn from this project and/or mentor? If you believe that academia is "about who you know and who wants you to get in," won't you be burning a bridge by declining this offer? Etc. Nobody here can give you an easy answer; this is something you're going to have to decide through introspection.