A gentleman and a young boy are standing by a door, looking expectant and impatient respectively.
"But daaaad," the child whines.
"Sorry son," the father said while shaking his head. "You'll have to wait until your mother comes back with that healing tonic before I let you outside."
"But! But! My friends are waiting for me, we were going to play Tonberry, and it needs all six of us!"
"If you got unlucky and got Firaga in that nick on your finger you wouldn't be playing anything for a week, and anyway she shouldn't be long now."
"I don't see why I couldn't get Curaga in it just as well..."
"Of course you'd get Cure in it, that spell is used so much that you're probably getting some in you as we speak. Even without the tonic, it'd only be a few days for it to heal up. But you'd probably get other spell fragments in it if you went outside where the winds carry them about, so just be patient and wait for a bit."
A pause in the conversation as the child thinks entirely new thoughts - to himself - about how people get sick, and why it always seems that...
"Dad, why is it that only Fire is dangerous?"
"Oh, it's not just Fire that is dangerous by any stretch son, it's just the most common by far. Fire can be useful for a lot of things, even if you're not fighting monsters, so of course people cast it a lot. And that means there are a lot of fragments of it around."
"Does that mean I could get Haste in my nick if I was unlucky? Or..."
"Indeed you could! Haste is a spell for experts, and I haven't seen its effects myself, but my grandfather - your great-grandfather - told me of a woman who fell sick and went to stay in bed for the rest of the week... Except, early in the morning next day she got up in a rush and ran around all over the house doing things she claimed 'Should have been done yesterday!' before finally collapsing from exhaustion. Her family kept her tied down in her bed for the next few days until she stopped yelling about how she couldn't just lie there, she had to take care of things nobody else would."
"That's right. You better be careful."
Another pause. This time the child starts looking more worried by the second.
"What're you thinking of now, son?"
"What about... what about Doom, dad?"
The father nodded, understanding the reaction.
"That spell could scare anyone. Thankfully it's very rarely used, but... Sometimes, people who were healthy one day seem to get tired unnaturally fast the next, and the following day they're bedridden. There are no visible signs of illness other than their exhaustion, they just... fade away. But don't worry about it son, it's so rare that you'd be more likely to trip over your feet and break your neck!"
The child didn't seem very comforted by this.
"Er, and I've never seen that happen, either, is what I meant. Just, don't think about it too much since there's nothing more to do about it than what I've told you; stay inside until your mother comes home with that tonic!"
Now at least slightly calmer, the boy returns to waiting for the family matriarch to come back and rescue him as the father lets out a silent sigh of relief.
A/N: Just an idea that came to me as I woke up.
If the spell fragments are the actual cause behind sicknesses in the final fantasy universes or if it's just their explanation (lacking science and microscopes) using concepts they understand, is open for debate.
Thanks to Puja723 for beta-ing!