An experienced Whitney hand asked me where I thought the halfway point is on the trail and I replied that Trail Camp is probably close to half way. I was corrected and told that in his numerous Whitney experiences he'd found that the summit was halfway. I would have to agree with his logic and would say the the worst miles are the ones you are not prepared for. Those may be the miles above trail crest, which I personally found to be a pain, the last couple of miles coming back to the portal, which can be very steep and very tiring after twenty miles of hiking, or any of several other notorious spots. I found that a lot of it is mental and it depends upon upon your attitude. I had a good summit trip recently and we had prepared with a few toough conditioning hikes. For me the switchbacks were a lot easier than I expected. The key is having a good attitude and believing that your goal is attainable. Also keep in mind that your goal is not the summit, but the summit and back to the portal.