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.