Let me elaborate it a bit:
Meet Mr. Virat Kohli. Chubby, foodie, occasional drinker, and highly aggressive.
Now meet Mr. Virat Kohli. The fittest cricketer right now, and with controlled aggression.
Do you think Virat Kohli had to leave his comfort zone to achieve this fitness? Yes, absolutely. If you read on internet, he stopped eating his favourite dishes, drinking, and did not rest even after scoring hundreds.
But do you think he still has to go out of his comfort zone daily to stay this fit? No.
What I mean is, he has made these things his routine. The very word routine used here clears that he is now used to these things.
Do you see the pattern? The same things he did few years ago were out of comfort for him, but those same things have now become his routine!
Looking this from my perspective, we never actually go out of our comfort zone, we simply expand our own boundaries of comfort.
To conclude in one sentence: It is often the fear of staying out of your comfort zone for long time that stops you from trying out hard things.
How do you push yourself out of comfort zone?
Simply identify your fear. Initiate to work on it. Keep repeating. And now It is in your comfort zone.