During a discussion with an Appalachian Mountain Club (AMC) backcountry caretaker (a worker who supervises tent platforms and composting operation at remote tent sites scattered throughout New Hampshire and Maine), this individual mentioned he had witnessed a packing style which he referred to SUL, or Stupid Ultra Light.
The reason for this slanderous term involved two northbound Appalachian Trail thru-hikers who, once they arrived in Hanover, New Hampshire, had decided that they were going to carry a bare minimum in pack weight in order to hike in a fast and light style through the Whites and Maine, on to their final destination of Mt. Katahdin.
The disconnect came when the pair chose to ditch their sleeping bags and insulated clothing, since they were traveling in the "summer" month of August. By the time the two had arrived after dark at the Imp campsite, they were hypothermic and in dire need of assistance from the caretaker mentioned above. The AMC employee ending up staying up all night brewing tea and letting them borrow any spare clothing and insulated items he had on hand to stay warm. Unfortunately, this left the AMC worker with a bit of a sore spot regarding UL/SUL because of these two hikers' irresponsible actions.
Understanding his point of view, we both agreed that insulation and clothing systems were something to take very seriously, depending on the region and time of year a person might be trekking.
Each year, I have run into a small number of backpackers going out for an overnight trip, and at the last minute they decide against bringing a sleeping bag. Their logic is that it was warm where they drove up from, and they will be housed in a warm tent...therefore, a blanket should be all that they might need. Unfortunately, this seems to be a common theme with hikers unaccustomed to summer months in the northeastern mountains. The outcome is usually the same: a cold and sleepless night spent shivering, leaving the hiker with a miserable hike out.
The proper clothing, combined with a sleep system to get one through a twenty-four-hour period, factoring in the nighttime low temperatures for the specific area one would be traveling through, are my most essential items.