Evan Green,
I think there are several types of "difficult"
Surely, the first hole at Prestwick is difficult, for a variety of reasons, but, I'll birdie that hole far more often than I would birdie the first hole at WFW. On the other hand, I'll probably make more double bogies and higher at Prestwick than I will at WFW.
Any opening hole with out-of-bounds or significant water in play is difficult.
In medal play, the short first hole at NGLA can be a birdie or a triple bogie.
First holes that focus the gallery, players and staff on a golfer create additional difficulties. The first at Merion, at lunch time, is one of the most intimidating, as is the first at Riviera, Bethpage Black and many others meeting the above criteria.
Each golfer also has their own criteria for establishing difficulty. A fader or Slicer won't like Prestwick, Quaker Ridge and others with dire consequences left. A pull slicer sure won't like Plainfield or Ridgewood's west nine starting hole.
Added to the mix are courses with no range, or a far removed range, where the golfer hasn't had a chance to warm up, especially at a course with a recognized, difficult first hole.
Lastly, the brain and negative thoughts contribute to difficulty. When a fellow golfer recounts how he made a 9 on such and such hole a month ago, and gives you a blow by blow of the blowout, that bit of information may overload the golfers mind, leading to further disaster.
Difficult holes are determined by the golfers particular game, their headset, the position of hazards/obstacles/boundaries, and their dislike of the spotlight.
Once it's in the air (assuming it gets there) there's nothing you can do, so Think POSITIVE, Take dead aim, and rip it.