The way it was explained/taught to me is that if Hashem wants you to have something, you put in hishtadlus to actualize your bakasha, and at the same time you understand that it is Hashem’s doing and not yours that decides.
It isn’t about “upsetting” G-d by doing His job, it is a matter of thinking that it really is in your hands after all and more hishtadlus would make it a better chance.
When you say you want to achieve your objective, the question is, do you really want to achieve YOUR objective, or do you want what Hashem believes is good for you? Should He give you things because you asked, or do only that which is best?
Hishtadlus, as I understand it, is about putting forth the effort to show yourself and Hashem that you are not expecting open miracles (something for nothing), but putting in repeated efforts may just be a show of thinking the efforts are the source. When the Rabbi said that you ‘could if you want’, I think he was assessing where you were at (as you asked) and assumed that if you did not put in more effort/hishtadlus, you may worry, ultimately, that a negative outcome was due to lack of effort and he was sparing you that anxiety.
I know it is hard to squish such a ‘big’ subject into a small space so I may not have been too clear, but I figured I would make my hishtadlus and hopefully Hashem will make it understood 🙂