Having lived the accumulation phase and now the semi Re phase, I can say it definitely helps to have dual income earners and be upper middle class. In fact i think that is who FIRE is designed for and where you hear of most success stories.
FIRE is not designed for the poor unfortunately. It's not for the wealthy/rich. They don't need it. It's really not for the middle class although it could work. This is where you see the extremes of FIRE and where I could see the most regret. It's really for the upper middle class. And really all it takes is living below your means for a certain amount of years. For me, I've lived in one of the best suburbs not only in Texas but in the US, flower mound. I pay 2k a month for mortgage and another 500 for bills and live in a great neighborhood. We go on 2-4 trips per year to mexico, both resorts and family and had no cares in the world for money while saving. It honestly wasn't hard at all to do this. All it took was saving excess cash diligently each month for 7 years and avoiding lifestyle creep. I never cared to keep up with the jones. The accumulation phase was actually quite painless. As for the FIRE phase, so far I am loving every second of it and am so proud of what I did and am now reaping the benefits. 5 days off a week is glorious and my off days are filled to the brim.
I think dual incomes of 100k or more each can easily achieve fire in 10 years while living a comfortable mostly upper middle class life. The dual incomes also imo relieve the stresses of money. It did for us. Our standard of living was set to 1 income. That way if one of us lost our job it wouldn't affect us. I think being the only earner could cause someone who wants to achieve fire quite a lot of pain and suffering. And all it takes is one person saving. My lovely wife spent her excess money and saved about 5k a year. It didn't make a shit. Just be sure to invest in the market. Nothing fancy. SPY or VOO will get you there.