Five, back to your boss questions.
I'm thinking that you need more information about why exactly your boss wants you to take on new small projects that you're not interested in. I'll presume that he thinks he's looking out for your best interests (rather than his own interests...e.g. dumping more work on you). For example, there could be external issues about the company that you may not be aware of (e.g. you could be maybe getting bought out and these extra experiences would poise you better to stay or leave) or maybe he wants to promote you and can't justify it unless you obtain these new experiences. Or maybe he's getting pressured from other people in your workplace to make you do different things. Or, as you surmise, he thinks it would be in your interests to move outside your comfort zone because....well...just because...you oughtta. So my first response is to suggest you try and get more info out of him as to what exactly are his motivations for pushing you in this "small extra job" direction. (Course, being a 9, if this involves confrontation or interpersonal difficulty, he may not want to be direct with you.)
My second thought is to see if it's specific projects he wants done, or if instead it's a set of skills he wants you to obtain or develop more fully. For example, maybe you don't like to write and he wants you to produce a technical manual for something (I don't know what you do, so I'm just grasping for examples.) so you'd become more at ease with writing. Or maybe he wants you to show more initiative, or execute higher level planning--I don't know. If it's skills he wants, then maybe some of these could be developed within the context of what you're already working on.
My third thought is to level with him....for example, maybe say that if you take on projects you're not interested in or motivated to do, this will sap your energy and effectiveness regarding the work you currently do well. He might not appreciate this as a possible consequence. Many bosses can deal in terms like efficiency, effectiveness, accomplishment, etc. (Course, being a 9, he's going to care about interpersonal harmony, compromise, agreement, etc.). While it might be good, in theory, to develop areas of weaknesses, I think that if you're an aspie, it probably works better to develop areas of strength. You can make this point without saying you're an aspie...but rather that you're more effective and HAPPY when you play to your strengths, which are...<fill in specific strengths with examples of how these benefit your employer>.
My fourth thought is .... stall...(if you haven't come up with a plan that you both accept as viable). Wouldn't recommend this if your boss were an 8 or a 1 or a 3 but a 9.......stall and maybe he'll just give up or forget
My fifth thought is to see if it's possible to agree on a plan you can both live with. Perhaps there are solutions you all haven't thought of yet. But this won't be productive, I don't think, until you get a better grip on where he's coming from in wanting you to take on these small projects.
Dunno if this helps any.
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Me, I have a 7w8 boss whom I basically like and respect but who, on occasion, drives me bats with his ever-varying "let's do this, let's do that, let's write a 60 page grant in a week, etc". He also pushes me, with varying resistances on my part, to get outside my comfort zone. I often feel as if I'm disappointing him because I don't sign on with exuberant enthusiasm to his latest pie-in-the-sky brilliant solution to inventing the future. I swear, this guy brings out the "provocative cynic" in me, so we have some good arguments sometimes.