I had gastritis (duodenitis, in fact) a couple of years back, and the first thing they did was test me for H. pylori. I didn't have it. Doctor told me a vast majority of people with such issues do.

After a gastroscopy, they concluded that it was just stress and nothing else, but inflamation wouldn't heal on its own, so I got pantoprazole (PPI) and stopped ingesting potentially irritating food (caffeine, alcohol, spicy food). I also shortly changed jobs, which alleviated the stress. Mind you, I never had heartburn, just pain. My condition didn't improve for a while after that, until I stopped drinking carbonated water (the only carbonated beverage I consumed), that fixed it in less than a month. After that, I gradually weaned myself off of pantoprazol in 6 months.

There literally was no other probable cause except for stress (I was stressed, wholly self-induced), and after I switched industries and no longer felt that I'm wasting my time working for peanuts, the PPIs helped cure the symptoms.

A perhaps easier to understand explanation of this is this part of a Robert Sapolsky talk on stress, prepositioned to the bit where he talks about the interaction of stress with the bacteria [1]. The summary is that the body is good at repairing the damage the bacteria do, unless the person is under constant stress which inhibits the repair work.

[1] https://youtu.be/D9H9qTdserM?si=bLeu9PmUgcCEAT41&t=1759

What is a bit of a myth? Sounds like stress is a factor but the bacteria is a direct cause in 90 percent of cases. The myth was that stress is "the cause".

what stress exactly? will a bad breakup cause ulcers? will hitting the gym cause ulcers?