Should you keep your startup idea secret?

I recently facilitated Startup Weekend Hawkes Bay, the first such event in one of my favourite regions of New Zealand.  Most of the people there were first-timers, and they put in a fantastic effort.

Just after the final presentations, one of our esteemed judges and local hero Sir Graeme Avery decided to give an impromptu speech, exhorting people to keep their ideas close to their chest:

Sir Graeme has built businesses around medical publishing and food and beverage.  It might make sense in these verticals to have everything planned out before you go public, but I don’t believe that this is the case for most online startups.  Your idea is important, but it’s all about execution.  I don’t think many businesses are going to be able to develop a sufficiently big first mover advantage from Hawkes Bay or New Zealand that will outweigh the benefits of getting customer feedback from a Minimum Viable Product as soon as possible.

Apologies to Sir Graeme if my interjection seemed rude.