I originally said this about classical music performance, but I am finding it just as apt with regards to fitness:
"It never gets easier. You just get more comfortable working hard."
Last month, I spent all month on the rowing machine (virtually rowing across Lake Erie, because these are the goals I will drag myself to the gym when I feel like ass to keep, apparently). This month, I'm virtually swimming from Europe to Africa, and when I got into the pool, I was astounded by how much harder I could work, it felt like I could fricking grab hold of the water and just pull myself through it. Instead of 25 strokes to make the length of the pool, it only took me 21!
Of course, it's because my shoulders are so much stronger from all the rowing... but I ended the workout much, MUCH more fashed than I normally am from swimming. Because I was strong enough to work really hard. I'm down 40 pounds, I have 90 more to go, and I feel like an Amazon.