Understanding Vocabulary in Context: Harrowing

Read the following excerpt:

"The old man sat on the porch, the weight of years pressing heavily on his stooped shoulders. He had seen many things in his time, some of which were beautiful, others harrowing. Despite the tedium of the afternoon sun, he found solace in the patterns of shadow created by the overhanging branches, each dance of light reminding him of fleeting moments he had clung to throughout his life. In his heart, echoing melodies of joy and sorrow intertwined, creating a tapestry of memories that felt both vibrant and melancholic, a paradox the old man had learned to embrace."

In the context of the passage, what does the word harrowing most closely mean?