Satisfy has these two Latin words as a root (from Google):
late Middle English: from Old French satisfier, formed irregularly from Latin satisfacere ‘to content,’ from satis ‘enough’ + facere ‘make.’
whereas fulfill has this etymology:
late Old English fullfyllan ‘fill up, make full’ (see full1, fill).
When something is full, putting more in will make it overflow.
So satisfy implies that there is a minimum to consider good, but you could do more to improve things further than the minimum.
Fulfill implies that either you achieved a standard (reached the "full" line") or did not. There is really no such thing as "halfway fulfilled," for example.
This is why things like destinies or orders are fulfilled, but not satisfied. Either you reached your destiny or you didn't, either your order is complete or it is not. But you could satisfy an indignant customer who didn't get an order fulfilled by giving him/her a gift card, though a higher amount gift card would make him/her more satisfied.
Best Answer
The difference between those two phrases is significant enough for each to know so they aren't confused in some contexts and close enough so they can be used interchangeably in other contexts.
When you introduce somebody who is going to speak in front of a audience, you say
meaning that aunt Betsie will say something she herself will choose and the number of the words is not known ahead of her speech.
An introduction to a commercial break on live TV by the host of the show used to sound like this:
Because they didn't exactly know what commercial advertisement is going to air but they knew it was supposed to be brief.
You use "some" as the determiner to allude to specific words without naming them:
In that case you either know or can give an example of those words. There are probably not very many of them, either, although the number is not necessarily "few" or "several", and generally speaking, the number is not determined by "some".
If, on the other hand, you say
you actually single out only a small number of words. Note the absence of "a" in front of "few".
When you refer to portion of the speech, for instance
you usually mean that you understood not all the words spoken, but whether that part is greater than a half or smaller, is not specified.
On the other hand, if you say
you certainly mean that only a rather small number of words were understood by you.
There are probably numerous other contexts in which the meanings differ.