Interestingly, Blake got that metaphor from Newton, which kind of undermines his protestations that Newton is his enemy. Newton said, famously 'I am but a small child wandering upon the vast shores of knowledge, every now and then finding a small bright pebble to content myself with while the vast ocean of undiscovered truth lay before me.'
This is one of my favourite quotes, and I think it explains what it is like to be an NT - a person who has iNtuition and logical Thought as their strongest characteristics - the N = the sea and the T= the sandy beach.
But in another twist to the history of this metaphor I did a quick Google to find the exact words of the Newton quote and the first two places listed were a Christian site called Evolution is Dead and an anti-religious site called Positive Atheism.
In other words - both sides think Newton is their friend. But Blake thought Newton was his enemy, although he probably wasn't. All based on the same metaphor, understood differently by different people.
*sigh* can you tell I'm bored at work today.