Learning a new language isn't hard because it's time-consuming. It's time-consuming because it's hard. The hard part is memorizing all of the details. Sure that takes lots of time, but working harder (more intensively) will reduce that time. It's hard to be dedicated enough to spend the time as well.
Getting a royal flush in poker isn't something I'd call hard. It's rare. But hard? A complete beginner can do that in their first try. It's just luck. But if you play a long time, it'll eventually happen.
Painful or unpleasant things are hard, because they require you to push through. Time-consuming activities are hard because they require dedication. Learning math is hard because you're outside your comfort zone.
Things are often called hard because achieving them is not common. Often because many people don't want to spend the effort needed. This is amplified by things like genetic and environmental differences. People rarely call riding a bike hard, but sure it required dedication and unpleasant experiences to learn. But surely if you're blind then it's way harder.
And lastly, things are hard because there's competition. Playing chess isn't hard, but getting a grandmaster title is. Getting rich is hard because of that, as well.
To extend this angle -- I notice that we're more likely to call things "difficult" when our expectations of whether we "should" be able to do it are mismatched from our observations of whether we are "able to" do it.
The "oh, that's hard actually" observation shows up reliably for me when I underestimated the effort, pain, or luck required to attain a certain outcome.
"time-consuming" does not cleanly encapsulate difficulty, because lots of easy things are time-consuming too.
Perhaps "slow to reward" is a better way to gesture at the phenomenon you mean? Learning a language takes a high effort investment before you can have a conversation; getting in shape takes a high effort investment before you see unambiguous bodily changes beyond just soreness. Watching TV and scrolling social media are both time-consuming, but I don't see people going around calling those activities difficult.
This study seems relevant here. It explores the idiomatic difference, from a Embodied Cognition standpoint, between the metaphor of "difficulty is heavy" and "difficulty is solidity" (and the inverse: easy = light). It is not the only literature on embodied cognition I recall to make the connection between difficulty and the physicality of lifting an object.
With this cross-linguistic study, we have come up with some findings regarding the status of two primary metaphors, “DIFFICULTY IS WEIGHT” and “DIFFICULTY IS SOLIDITY,” through both qualitative and quantitative evaluations of their linguistic manifestations in English and Chinese. While the linguistic findings do support the validity and applicability of the two primary metaphors in both languages, their linguistic manifestations, however, vary considerably in degree across and within language boundaries.
Ning Yu & Jie Huang (2019) Primary Metaphors across Languages: Difficulty as Weight and Solidity, Metaphor and Symbol, 34:2, 111-126, DOI: 10.1080/10926488.2019.1611725
I have noticed that when someone says that something is hard or difficult, this can mean several different things. I think I have broken it down to 3 categories:
Of course some things are difficult because of a combination of two or all of the above. Becoming president of the USA takes both lots of time, hard work, unsavory compromises, and the cooperation of many other people, plus you need to satisfy some requirements outside your control such as having been born in the USA.
Do you agree with the above categorization? Or have I left something out?
Thanks in advance!