Did your friend pass a kidney stone? I was on the top of Halfdome a few years ago when someone got airlifted off. It was really cool to see the chopper come up the valley, circle and land.

The hike up Halfdome is not a typical "day hike" it takes most folks pretty much all day (sun up to sun down in July and August) to make the trip. It is along a well worn trail and is very crowded much of the way but it also goes up to over 8K. I think it gains 4,000 feet of elevation along the trail.
Many folks get sick from altitude (flatlander tourists types), heat illness and dehydration. This hike would require you carry some water purification (you will run out of what you have been carrying), a headlamp or flashlight (not just a photon or aaa LED; I have hiked extensively with a BD Ion and it is a lot of work to "peer" into the darkness beyond your tiny beam for hours. Go with a brighter light.) and clothes for the cool night temps. If you don't prepare one might find themselves out of water in the dark and wet (Mist Trail / Vernal falls) for the last few miles of trail. Although there is a water fountain at the bottom of Vernal falls.

This said; every hike has to be considered on its own merits. I have done the 1/2dome hike several times including approaches and descents from climbs on the dome(this involves cross country travel). It can be a serious hike even for the strong and I have seen both tourist and climbers alike getting schooled. So this hike warrants a decent amount of gear.
On the other hand a hike in the local park in the Berkeley / Oakland hills for a couple of hours for example barely rates anything but a modest EDC a jacket and a bottle of water.

Some folks go through a process while learning to hike and backpack where at first they are woefully unprepared then they pack too much gear and ultimately they get it to a manageable and realistic load that is appropriate for the outing.