Good writing is all about word choice in a specific situation. Some words you’d use in formal writing would not be (emphatically not be) what you’d use when writing, for example, colloquial conversation.
Here are three words that people seem to use interchangeably, but really do have shades of meaning that make each a bad, good, or better choice, depending on your audience.
Difficult, hard, and tough are three words I see being used interchangeably, with hard and tough seeming to be more common. I’m not sure why, unless it’s because “hard” and “tough” are words of one syllable: the old dumbing-down-your-writing ploy.
Let’s look at these three sentences:
Changes in your loved one’s visual and spatial abilities may make it difficult to distinguish food from the plate.
Changes in your loved one’s visual and spatial abilities may make it hard to distinguish food from the plate.
Changes in your loved one’s visual and spatial abilities may make it tough to distinguish food from the plate.
Of the three, the first sentence is the most precise: the writer is talking about the challenge of distinguishing between two different things.
The middle sentence, using hard, is not as good as the first, because hard  means impenetrable, solid, etc.
The third sentence is the worst, the most slangy, and the least appropriate for formal writing, especially not for an Alzheimer’s nonprofit’s website, which is where I found it.
What is it “they” say? Write to a third-grade level?
God help us all.