The most danger of packing inadequate items can easily not come from experience but from other influences such as magazine articles, TV shows, even fictional movies can influence a persons taste or preparations.
While I am now old and aware of each pound I have to carry in my pack, I was not always that way. I still am not one to cut off my toothbrush handle to save a tenth of an ounce. I can gain knowledge from some of the fast/light hikers but I have to take care to apply my experience in a careful thought process that helps me make wise decisions on gear and what to carry.
Example: a few years ago I want on a backpacking trip and had to carry all my own stove, tent, etc. The tent I chose is one that was very popular with the ounce counters, I won't name it's maker but it was basically a tarp with some netting and a floor. I set up the tent just before it started to rain and layed inside to keep dry, late afternoon. I kept feeling colder and colder and finally decided I needed to get up and do something to warm myself. What I discovered is that I was laying in a puddle of water in the floor of the tent and my sleeping bag that I had been using as a pillow in it's stuff sack had also gotten soaked. I looked at the cause of this inconvenience and discovered that the design of this particular tent would allow, even promote the water to flow in if the rain came from a certain direction. Something that is hard to control since it started raining after the tent was set up. Design compromise was to save weight some features were not what they should have been.
I have not used that tent since and never will again. Saving a pound is not worth the potential serious consequences.

All this had little relative value to the incident on Ranier but the point is sadly we often make decisions based on input from sources outside our own experience and should take care to apply our own knowledge and the knowledge of others and make wise choices of gear to carry and not just take what someone else recommended. If a popular method for climbing a route was to carry a bivy bag and no real insulation does not mean it will work 100% of the time for every climber. Metabolism varies as will conditions. I would not consider just a bivy and my clothing for a high altitude alpine climb, based on my times on a big mountain and what I know I need to stay warm.