“Close observation of life is critical to good writing, said Hemingway. The key is to not only watch and listen closely to external events, but to also notice any emotion stirred in you by the events and then trace back and identify precisely what it was that caused the emotion. If you can identify the concrete action or sensation that caused the emotion and present it accurately and fully rounded in your story, your readers should feel the same emotion. In Death in the Afternoon, Hemingway writes about his early struggle to master this:

I was trying to write then and I found the greatest difficulty, aside from knowing truly what you really felt, rather than what you were supposed to feel, and had been taught to feel, was to put down what really happened in action; what the actual things were which produced the emotion that you experienced. In writing for a newspaper you told what happened and, with one trick and another, you communicated the emotion aided by the element of timeliness which gives a certain emotion to any account of something that has happened on that day; but the real thing, the sequence of motion and fact which made the emotion and which would be as valid in a year or in ten years or, with luck and if you stated it purely enough, always, was beyond me and I was working very hard to get it.”

Source: Open Culture