I've always hated this saying, and I think the reason applies here too.
If you take up running and it never gets easier, that means you're never managing your pace and you're always going full throttle. That's a straight shot towards injury if not chronic disability. Most aerobic benefits happen at zone 2, where your heart rate is just above 'easy effort'. When you start out, this might just be walking, so it makes sense to run. But once you are able to sprint, you open up the ability to do more than just walk or sprint. You can jog, skip, run at a tempo pace, run at a race pace, etc., and you need to do those to maintain fitness and build up your chronic training load. That's not to say there aren't hard efforts at times, like when you do a sprint workout or hill repeats, but 90% of the time it should be and feel easier than when you started.
You can bring that to programming too. If it never gets easier, that means you're always pushing yourself and seeking challenges. That's not good for you, your coworkers, or your projects... everyone needs some grounding and to perform at a level they excel at. Not only will your velocity be more predictable, you won't burn out as easily. Challenges that increase that comfortable pace can be sought out, but usually they come naturally too.
Lemond's statement is in reference to racing. The race isn't won in zone 2. Same with programming. Nothing wrong with a lot of zone 2 programming, in fact it's quite important to maintain balance like you describe, but the race isn't won with comfortable work.
I’ve seen my share of programmers who showed off all-nighters and productive weekends, only to realize they compensate but not actually working productively their entire 40 hours, not even half. Programming is not a race, it’s a marathon.
My issue with the 40 hours is the constant interruptions with meetings, co-workers asking questions, shifting priorities, etc.
When pulling an all-nighter or weekend, all of that stuff goes away.
It’s been a long time since I pulled and all-nighter or weekend, but I’ve been thinking about it just so I can feel like I finished something. If I could get actual heads down time during my 40 hours, I’d much prefer to use that time.
I’m too burned out from the 40 hours of BS. When I have a couple weeks off I usually get inspired to start a side project. I get started, then in quickly dies once I start back up at work. I hardly touch my personal computer anymore.
The saying resonates with me. I have different problems programming now compared to when I started. But I still bang my head against a wall until it gives or I leave with bruises. I may not notice the little walls I step over now, and I learnt which walls to respect. The easy stuff I do on the side.
