It's worth noting that if you go fifty years back or so, fountain pens and dip pens were a lot more similar to each other than they are today. Both typically had flexible nibs and the real difference between them was just whether the ink automatically flowed from a reservoir inside the pen or was manually collected from an inkwell once in a while.
(okay, yes, also the inks themselves were completely different, with fountain pens having to use dyed water solutions to avoid clogging the pen, whereas dip pen inks actually have solid particles of pigment held in suspension in their ink, giving bolder colors and darker blacks when dry on the page; if you put a dip pen's ink in a fountain pen it would very quickly clog up with those pigment particles. And back in the day, it would probably eat right through the latex bladders the ink was stored in)
The fountain pens you get today are very different from the ones back then; they have stiff nibs which can survive the sorts of pressures that ballpoint users are used to inflicting on their pens, and they're equipped with quick-drying ink. They're pretty much indestructable under normal usage. But back in the day a fountain pen required a very light touch and some patience (or blotting paper) to ensure the writing didn't smudge and that you didn't damage the nib.
(there's been a mild resurgence in the popularity of flex nibs in fountain pens over the past few years. I haven't seen any which have anything like the flexibility you see in real vintage pens, but it's a lot more than we've seen in fifty years and it's nice to see them making a modest return!)
(okay, yes, also the inks themselves were completely different, with fountain pens having to use dyed water solutions to avoid clogging the pen, whereas dip pen inks actually have solid particles of pigment held in suspension in their ink, giving bolder colors and darker blacks when dry on the page; if you put a dip pen's ink in a fountain pen it would very quickly clog up with those pigment particles. And back in the day, it would probably eat right through the latex bladders the ink was stored in)
The fountain pens you get today are very different from the ones back then; they have stiff nibs which can survive the sorts of pressures that ballpoint users are used to inflicting on their pens, and they're equipped with quick-drying ink. They're pretty much indestructable under normal usage. But back in the day a fountain pen required a very light touch and some patience (or blotting paper) to ensure the writing didn't smudge and that you didn't damage the nib.
(there's been a mild resurgence in the popularity of flex nibs in fountain pens over the past few years. I haven't seen any which have anything like the flexibility you see in real vintage pens, but it's a lot more than we've seen in fifty years and it's nice to see them making a modest return!)