Chris Mamula does a lot of writing about having retired early, looks like he was 41, and his latest post (I found it at Yahoo) covers some important ground about the concept of financial independence replacing the idea of traditional retirement.
I take his post as saying he was very unhappy with what he was doing and that he was desperate to make changes which he was able to do at a young age. He offers some actionable thoughts on how to get there slowly if slow is the only realistic option. His first suggestion is to figure out what you really want. This is something I have been saying for years as I think it is an obvious point. It can help you avoid killing yourself for the wrong outcome. My wife and I don't desire a McMansion with two new BMWs in the garage as a cliche example. We were admittedly very lucky that we figured out what we did want at a very early age, still in our twenties.
Chris talks about making improvements in your work situation. There might be things that an employer might be willing to do to make you happier if they are not too costly. He talked about his having traded future raises for more vacation time when he was working. There are a lot of different ideas, success would likely come from understanding what is important to your employer and what isn't important, clearly this might be difficult to figure out but it is possible. He also talked about the leverage you have when you're willing/able to walk away. From the employer's viewpoint, replacing someone who knows the ropes can be difficult which is a negotiating asset if used effectively.
All of this is easier when you live below your means. In addition to saving more it means there is less of a monthly nut to replace. A $1500 mortgage with no car payments gives a lot more flexibility than a $3500 mortgage and paying for those two beemers. Part of what contributes to unhappiness for a lot of people is worrying over money. You're less likely to worry about money if your fixed monthly expenses require less of it. While you might think it is an obvious thing to say, look at how many people have no savings and look at all the news sources lately that are reporting increasing levels of consumer debt.
These are stressors that make it more difficult to get to where you want to be whether that is early retirement, or the flexibility to change to a more fulfilling even if lower paying job in your 50's.
The article closes out with something I've also been writing about for years; deriving some sort of post-retirement, part time income like from monetizing a hobby. I've written countless times about bailing out an undersaved retirement by downsizing into a tiny, or small house and figuring a way for both partners to earn a combined $1000-$2000. This sort of planning, whether it's what Chris is writing about or what I am writing about can't wait until you wake up on day one of retirement. It has to start many years before retirement. As Joe Moglia said, no one will care more about your retirement than you.