But while I do think appreciating what you have is part of how to avoid the hedonic treadmill, I don't think it's a matter of learning to be happy with a routine.
I've found it possible to make a conscious effort to avoid hedonic adapation, and enjoy novel things without allowing them to become a new baseline. If you can maintain your expectations at the same level, while improving your actual circumstances noticeably above that level, you can maintain a higher level of enjoyment of your life.
Single, full-time working people, especially in tech, start to unlock the ability to travel abroad, maybe even one of those big two-three week Life Changing things to somewhere exotic, but only once in a lifetime or once every few years.
Middle / upper-middle class incomes eventually get to a point of wealth and freedom where they can take vacations abroad multiple times a year.
And I think you need to be even above that level, where you don't have to worry about your base income or mortgages or whatever, where you can have this lifestyle where you can have novel things and experiences all the time. And even then there's a risk people get used to it.
Even with very little means you can travel and see the world. It’s just a matter of priorities and what kind of life you want to make for yourself. If you think you have to establish the standard life package first and then go see the world when you have spare time and money, sure, maybe you won’t until you’ve made it pretty far. Right out of high school, instead of going to university, I decided to travel abroad. I didn’t have family money. I’m from a poor family in a small town. I just saved a little money working service jobs and traveled on the cheap. CouchSurfing, hitchhiking, camping out, hostels, etc. I’m not special. My little sister is doing the same thing now on waitress money. I’ve met countless people out on the road living interesting and meaningful lives, traveling abroad without being a single, full-time tech worker. You just have to ask yourself whether you need to compete materially with everyone who’s staying in one place and accumulating stuff.
To think you only deserve a couple Life Changing, two or three week trips, even as a high earning tech worker… Such poverty of spirit makes me depressed just thinking it. Consider a few great authors, like Orwell for example. As a broke 20 something he was tramping around living a series of great stories. If he’d chosen to play it safe, stay home and work at some Important Career and collecting stuff, he’d probably never have gone to Spain in 1936, and the world would probably never have received his most important works as a result.
How does one live this lifestyle with children and/or other dependents, such as an elderly & infirm parent or a permanently-disabled sibling?
A lack of obligations is another kind of wealth; a privilege, even. I guess only people like you can afford to rise above this "poverty of spirit".