Originally Posted by
Trakhak
Compression plugs see only a small amount of force, since the only requirement is that they allow setting the preload on the headset bearings.
Same deal for the custom shim. All you had to do was get the dimensions right. And little or no chance of failure if you got them wrong.
The conclusion in that thread and elsewhere was that at least in carbon steerers, it needs to reduce compression forces imposed by the stem (and doesn't merely serve to allow preloading), which is why people were saying that it was crazy advice to go with a DIY solution. Whether or not you are right about the shim, the advice then was to get a new fork to save myself a great deal of (physical!) pain.
In general, I think most points of failure on a bike can be pretty catastrophic (don't ask me how I know). Bars, stem, and fork are especially bad news, but severe tyre blowouts, tubular rolls, chain breakages, and crank and pedal failures can be pretty serious if putting down the power standing up. Honestly, along with certain types of frame failure, a seatpost breakage would probably be among my top picks! I had a clamp bolt fail once, at which point the (too small) seatpost instantly telescoped into the frame, and I was surprised that the reflex fully caught me, my legs taking the load immediately without my going down with the plummeting saddle.
Re the seatpost you mention, the problem has been that I need a 25.0 mm seatpost (Look, Vitus, etc.) and not a 25.4 mm one. Luckily, the bike is in action with the alloy setback post I have, so I can take my time on this current project and do it right.