I described a rig failure due to a missing or failed cotter ring on a Venture a year and a quarter ago:
Cotter rings and some other trivial pieces of hardware are what hold the boat together. When you have two parts of the boat coming together, like a shroud and the deck fitting, there's usually a pin doing the job and something like a cotter ring preventing the pin from coming out. It could be a shackle or a lock-tight nut, but it's usually a cotter ring or Cotter pin.
It's hard to over-emphasize inspecting these pins before you take the boat out, as failure on the water can ruin your day (see above). I don't think many of our Junior skippers or even, dare I say it, all of our Senior skippers would have been able to get control of the dismasting situation and sail the boat home.
When I teach boat inspection, I talk about this and tell the students to find all of the cotter rings or other things and determine whether they're sound, and I explain how they fail and what to look for.But on the RS Venture, there's what I now call the Mystery Ring, which is what failed in the cruise I referenced above. If you don't know it's there, you'd never check it. That's how it happened on my cruise....