One of the rules is to never offer your gold nib fountain pen to anyone. Gold nibs are soft and adapts to your writing style over the time that people who are not familiar with fountain pens but biros usually press too hard to the paper that alters the soft nib.

True, I use my nice pens in the office or at home. I've a Baoer 388 I carry around, apart from the lacquer that seems almost indestructible and writes very well.

I think I read a while ago that fountain pens don't wear to your writing style, that's an old tale. Pressing too hard will usually damage one though.

Depends on the nib. A 18K nib is soft enough to develop flatter surfaces over the time, based on the owner's writing style. It is also mentioned on one of the premier fountain maker's (and OEM nib maker) page: https://www.pelikan.com/pulse/Pulsar/en_US.CMS.displayCMS.25...

I can't see where on that link it talks about the nib developing flatter surfaces. The nib is flexible and with long term use and excessive pressure can alter the angle of the tines. That can affect the ink flow through the slit affecting how the ink is laid.

The tip, the only part which touches the paper, is made of iridium[1], or similar, which is very hard. As far as I can tell that doesn't wear. Some very old or specialise/custom nibs may use softer metals and perhaps wear would be a possibility on those but in any instance I can't see you wanting a flat spot to develop.

[1] It turns out that modern iridium nibs probably aren't made of iridium. I was looking into wear on them and found, amongst others, this https://www.nibs.com/blog/nibster-writes/wheres-iridium which does into detail analysing the composition of a fair number of nibs. Down the rabbit hole!

“As the material is soft enough to adapt to your handwriting with time.”

Not every nib is flexible. My Duofold and Meisterstück certainly aren't, my cheap Noodler's Ahab just to a limited extent (but it is a special steel flex nib).