Fine I'll bite :Þ
Have a poorly-ordered braindump:
In my life, I've kindof developed a rule of thumb: if it's the more difficult path, it's probably the better path.
That heuristic isn't always correct, but I find it to be pretty good. Problems can arise when I follow it blindly, though.[1]
I've just generally found that a lot of good things in life are on the other side of a barrier, and crossing that barrier usually involves effort and pain.
So, it starts to develop into an association of "if it's hard/painful, it's probably leading somewhere good."
And that starts to develop into "seek out pain/difficulty."
Ironically, I'm also someone who values being comfortable in my own skin.
But I feel more comfortable doing something painful for my own (masochistic?) reasons than doing something painful for an external goal.
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I do feel like there's often an element of masochism in people who excel at some activity. Plenty of stories of top athletes or musicians etc. who do it for their own reasons, and not to win a trophy or acclaim. Getting good at something is generally a painful process of dealing with failure over and over. If you don't have a stomach for that pain, you'll give up. If you grit your teeth and force your way through it, you may become competent, but probably won't excel. If, somehow, you enjoy that pain and are drawn to it, then you will put in the hours to keep getting better and better, unboundedly.
But that's just one perspective.
The grandparent comment seems more like someone who likes to "keep their eye on the prize," whereas I'm more of a "do it because I enjoy[2] it" person. I suppose if you are motivated strongly enough by some external goal, it could push you through the hard times, too. And if the goal keeps moving, you might keep pushing, unboundedly, too. Not my path, though.
See also "Type 1,2,3 fun", eg: https://essentialwilderness.com/type-1-2-and-3-fun/ (definitions vary)
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Also, I find taking a hard path is sort of a Great Filter for other people; there will be fewer others on that path (I'm fairly solitary, so it suits me), and what people there are will have something in common with me.
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[1] When I hear about people trapped in abusive relationships, trying to "fix" it rather than leaving, I feel like I understand them somewhat. At the same time, some relationships are worth saving, even (especially?) in the hard times, so being able to navigate the pain rather than run away can a strength, too. Depends on the situation.
[2] with "enjoy" being somewhat perverse, at times (: