- Haven’t X, Y, and Z already done this? We shouldn’t be supporting duplication of effort.
- Are all of the stakeholders on board? (Hat tip to @patrickgmj for this gem.)
- What about sustainability?
So, some ideas for countering these when you're working on your proposal:
- Have you looked at work that's been done in this area (this might entail some real digging)? If there are projects and/or literature that deal with the same areas as your proposal, then you should take them into account. You need to be able to show you've done your homework and that your project is different from what's come before.
- Who is your audience? Have you talked to them? If you can get letters of support from one or more of them, that will help silence the stakeholders objection.
- You ought to have some sort of story about sustainability and/or the future beyond the project, to show that you've thought about what comes next. Even if your project is an experiment, you should talk about how you're going to disseminate the results so that those who come after will be able to build on your work.
I agree with Tom that these criticisms can be deployed to stifle creative work. In technology, sometimes wheels need to be reinvented, sometimes the conventional wisdom is flat wrong, and sometimes worrying overmuch about the future paralyses you. But if you're writing a proposal, assume these objections will be thrown at it, and do some prior thinking so you can spike them before they kill your innovative idea.