Pyramids in Oceans

When it’s going good, it’s like building a pyramid,
hauling blocks and hoisting them in place,
fitting each neatly into my construction,
each supported below and supporting above,
until I lay in that last capstone, the pointed one,
the in the end it all comes down to this conclusion, 
so finally sit atop the perfect structure I’ve designed.
And at that point I may realize it’s not a pyramid at all,
but an iceberg, and I can see only that 10%
bobbing above the dark freezing deep water.
When it’s going great, I’ll come out of my writing fog
and find to my amazement I don’t understand the other 90%.