A speaker goes up to a high place to get away, and stays there until something small and ordinary drives them back down: a hole in their coat. The poem moves quickly, in just a few short lines, and the plainness of that reason is part of its charm. Whatever grand feelings sent the speaker uphill, it's a worn-out piece of clothing that ends the retreat.
The last line, "I almost wrote," is the one that lingers. It suggests the speaker went up with some hope of writing, perhaps expecting the solitude to bring words, and it didn't quite happen. The word "almost" sounds a bit rueful and a bit funny. The mood is quiet, dry and gently self-mocking. There's real longing for stillness here, but also an honest admission that the body's needs, and our own hesitations, tend to get in the way of big plans.