How many users will you turn away? Do you think it will be a significant portion of your potential users? To be clear, don't you think it's worth having .05% of your total possible user base turned away so that you can understand what the other 99.95% want?
well, it's a tough one... Intellectually, I agree with you, but it's sort of a gut feeling. The issue is that as a start-up you are limited in resources. So how many campaigns can we run? How many friends can we nag to use our service time and time again? etc. You don't want to exhaust your resources at the beginning.
Of course we will launch and iterate, but this is just a fear. Is it rational? Maybe not. I hope not :-)
LinkedIn's founder Reid Hoffman once said: "If you are not embarrassed by your first release, you've launched too late!"
If you want to try stuff out early, also consider in-person guerrilla user testing, running ad-driven tests on a fake brand, buying low-cost traffic, and asking fellow entrepreneurs to try things out. For more on this, the Lean Startup Circle mailing list has a lot of good ideas.
