Well, last Friday was my last day at Uber, so I'm in the opposite position right now and am just starting as a Indie Hacker. But I think I can provide some interesting views.

I just spent 4 years at Uber. I joined early 2014 as the 99th engineer, when there were like 400 employees. Coming from a 10 people startup (Exec) it felt huge, but compare to today's Uber, it was pretty small.
Despite the size difference, the work at Uber then was pretty similar than the work at Exec, while we had only 2-4 engineers at a time. You still end up hustling, working your ass off and wearing a lot of hats. It's great.
It's hard work, both because you work a lot of hours, and the work is actually pretty hard and stressful, but it's also very rewarding. I don't think I've been happier in my life then my years at Exec/early Uber. Working very hard, late nights, weekends, BUT having a big sense of ownership. Not feeling like I was working for someone else, but really driving our own destiny. Being part of something and owning it. Knowing that if I screw up, it won't only be a small dent, but can have a huge negative impact. Just like if I succeed at something, it would have a great positive impact on the business.

So yes, very hard work, but very rewarding.
I never created my own business but I do believe how I felt then is comparable than when it's your own business.

If I compare that to the past 2 years at Uber, while we've reached huge valuations, over 10k employees (close to 20k now I think) and thousands of engineers - well, I don't really matter anymore. My contributions are smaller, less noticeable, even to myself, because impact is smaller. Early days I felt bad about taking vacations, because I knew finishing my projects earlier would mean a substantial increase in an important metric. Now, well I see plenty of people taking 3-4 months sabbatical and it's totally fine. I just quit. The project I worked on is going to be delayed by a few weeks until someone else finishes their own project and takes over, and it's totally fine. Nothing will change.

It's great in a sense. At that point I was even working remotely, so waking up and doing a good 3-4hrs of productive work in the morning was more than enough. No late work, no weekends. Ample vacation time. 0 stress. Good money.

But, I'm here now :) I quit. Why? Oh boy it becomes boring really fast.
This would work well for a lot of people (I guess most people just want to do the bare minimum and are happy), but chances are, if you are here, asking this question or reading those answers, you're not like that, and you are not interested in doing an uneventful, unimpactful 9-5. Just like, most of us here will not retire ever. Building, doing something, is part of us and what makes us feel good.

I just listened to Indie Hacker podcast #47, where Joel Runyon says "I'm 1 or 2 phone calls away from a job". He doesn't want that job. None of us want that job, but I think it's great to know that by being Indie Hackers, building experience, reputation and relationships, we are a phone call away of a job, in case anything goes wrong. But we don't really want that job :)