grammar - What is the reference of "it" here?

I've come across with the sentence below?

Old tasks become easier the second time around, but it doesn’t get easier overall because now you’re pouring your energy into the next challenge.

I don't know what the reference of "it" is here. The tasks? the process? or anything else? So could you please tell me what the reference of "it" is here?

The full text is:

Usually, this minor dip in performance is no cause for worry. [...] The less energy you spend on trivial choices, the more you can spend it on what really matters. However, when you want to maximize your potential and achieve elite levels of performance, you need a more nuanced approach. You can’t repeat the same things blindly and expect to become exceptional. Habits are necessary, but not sufficient for mastery. What you need is a combination of automatic habits and deliberate practice. Habits + Deliberate Practice = Mastery To become great, certain skills do need to become automatic. Basketball players need to be able to dribble without thinking before they can move on to mastering layups with their nondominant hand. [...] But after one habit has been mastered, you have to return to the effortful part of the work and begin building the next habit. Mastery is the process of narrowing your focus to a tiny element of success, repeating it until you have internalized the skill, and then using this new habit as the foundation to advance to the next frontier of your development. Old tasks become easier the second time around, but it doesn’t get easier overall because now you’re pouring your energy into the next challenge. Each habit unlocks the next level of performance. It’s an endless cycle.

Atomic habits by James Clear

Answer

That is rather like a "weather it". The sentence requires a subject and "it" is used without a definite reference.

You could interpret "it" to mean "The process of developing mastery", ie the subject discussed in this paragraph.