I don't know where I first heard this quote. It was probably Richard Feynman, the physicist, who was puzzling about the mysteries of quantum mechanics. But the older I get, the more I find myself saying this.
Quantum mechanics has a way of doing that. About this field, someone -- another physicist -- said that scientists don't really understand quantum mechanics, they just accept it. The equations work. So they fiddle with the equations in search of a problem, and presto chango, allakazamm, out pops the answer. The equations work, but everyone is left with a disquieting feeling that they are in the presence of something mysterious, because they can grind through the equations as if they understood the underlying principles, which they don't, and yet the mathematics is right. It's like the sorcerer's apprentice invoking an ancient and powerful chant, who unleashes a power he can't harness, something that's bigger than him.
My love is geometry, or, more generally, mathematics. There are many theorems that I stumble across that are completely non-intuitive at first presentation. But the longer I use them as new tools, the more they settle into my brain. If I wait long enough, they become obvious.
If you can prove a theorem three different ways, then it becomes obvious. Until you get there, it's not.
But wait!, you say. If this is your definition of obvious, then it's not obvious at all! This only means that it's sunk in, and that you've gotten used to it, but it's not a general obvious fact to the wider audience.
One of the great physicists - it was probably Wolfgang Pauli or Niels Bohr - was giving a chalkboard lecture where he filled the board with equations, and one step was such a leap that a frustrated follower had the temerity to ask the professor if that was step was obvious.
The professor stepped back from the blackboard, looked at it intently for a few minutes, hemmed and hawed, and then looked at the class and said, "Yes, it's obvious."
I always liked that story, because of the innate contradiction. I can only think, "Clearly, he's not using the word 'obvious' the way normal people define it."
And so when I plug along and learn something new, I look at something three different ways. I'm not content to have a superficial understanding of anything. But if I can show that something is true three independent ways, then it becomes...
... wait for it.... wait...
Ah yes, it's obvious!