Let’s be clear on the purpose of a proposal: to persuade the funder that you are a good fit for their money. A proposal is not to convince a funder that your idea is the best solution and the only way to address an issue.
Admittedly, this is a murky point because a grant application does need to convey the urgency of the need and that your program will have positive impact. You can, however, successfully convey these things by matter-of-factly describing your organization’s history and track record, showing the funder your passion and understanding for the issue with a well-researched needs statement, and clearly explaining exactly how your organization will achieve its goals using relevant data and SMART (Specific, Measurable, Achievable, Relevant, Timely) objectives in your project description.
If you write a proposal with the assumption that the funder is your target audience, you risk your application coming across as a hard sales pitch. It’s easier for you to unintentionally overstate your organization’s importance and exaggerate the expected success of the program.
Funders want to see that you are realistic about the need and expected outcomes of your program, so don’t get bogged down in trying to convince them that you have the best idea ever. You only need to convince them that you have a program worth investing in.