Two friends and I just spent 5 days in Yosemite, hiking from White Wolf through the Ten Lakes Basin, over Tuolumne Peak, and out via Murphy Creek. The scenery was stunningly beautiful. And I, still something of a newbie (though less of a newbie than my companions), learned a few things.
1. An extra 5 pounds in your pack makes an incredible difference in how hard it is to carry. Water sources were few and not always reliable, so I ended up carrying an extra 2.5 liters one day. It really made it obvious how much a few pounds can matter.
2. My ability to function tops out at around 9,500 feet. Up to that altitude, I noticed the lack of oxygen, but could compensate for it reasonably well; I just traveled even more slowly than usual. Above it, I had to walk as if I were 102 years old -- take a few slow steps, stop to catch breath, repeat. Even just standing up was a struggle. I grew up in the Rockies, but I'd not been over 7,000 feet or so in many years, and had no idea how well I would cope.
3. Perhaps I don't want to try a tarp after all. The zipper on my tent door failed, so I spent most of the trip with some large openings in my tent. I closed the rainfly, which kept most of the flying bugs out -- and unless those are really thick, they don't bother me that much. But some ants came to visit me in the night. They thought the inside of my sleeping bag was a fun place to explore. I disagreed, and they were summarily evicted. Fortunately they didn't invite all their friends to the party!