The people who lived in castles didn't need to farm or fish.
The Lord of the castle (generally appointed by the King) is owed a tithe (usually 10% of their produce) by the people living on his lands, and they undoubtedly had the task of delivering food and other goods to the castle throughout the year. In return he and his men provide "protection" to the farmers, artisans, merchants etc. in the event of an attack. People who do not produce useful goods would pay a tax.
The King would have some castles held by a Constable, who is not a true Lord in his own right, and the income from the lands controlled by these castles goes direct to the King. The Lords also pay a tax to the King, so he gets quite a lot of dosh.
That's a simplification of the Feudal system which took centuries to evolve, but you get the idea od a few rich lazy sods at the top of the pyramid, and a lot of downtrodden peasants at the bottom working their socks off to make ends meet and have enough to give to someone who owns the land they live on.
Sorry, Martin, but here's how it really works:
ARTHUR: Old woman!
DENNIS: Man!
ARTHUR: Old Man, sorry. What knight lives in that castle over there?
DENNIS: I'm thirty seven.
ARTHUR: What?
DENNIS: I'm thirty seven -- I'm not old!
ARTHUR: Well, I can't just call you `Man'.
DENNIS: Well, you could say `Dennis'.
ARTHUR: Well, I didn't know you were called `Dennis.'
DENNIS: Well, you didn't bother to find out, did you?
ARTHUR: I did say sorry about the `old woman,' but from the behind
you looked--
DENNIS: What I object to is you automatically treat me like an inferior!
ARTHUR: Well, I AM king...
DENNIS: Oh king, eh, very nice. An' how'd you get that, eh? By
exploitin' the workers -- by 'angin' on to outdated imperialist dogma
which perpetuates the economic an' social differences in our society!
If there's ever going to be any progress--
WOMAN: Dennis, there's some lovely filth down here. Oh -- how d'you do?
ARTHUR: How do you do, good lady. I am Arthur, King of the Britons.
Who's castle is that?
WOMAN: King of the who?
ARTHUR: The Britons.
WOMAN: Who are the Britons?
ARTHUR: Well, we all are. we're all Britons and I am your king.
WOMAN: I didn't know we had a king. I thought we were an autonomous
collective.
DENNIS: You're fooling yourself. We're living in a dictatorship.
A self-perpetuating autocracy in which the working classes--
WOMAN: Oh there you go, bringing class into it again.
DENNIS: That's what it's all about if only people would--
ARTHUR: Please, please good people. I am in haste. Who lives
in that castle?
WOMAN: No one lives there.
ARTHUR: Then who is your lord?
WOMAN: We don't have a lord.
ARTHUR: What?
DENNIS: I told you. We're an anarcho-syndicalist commune. We take
it in turns to act as a sort of executive officer for the week.
ARTHUR: Yes.
DENNIS: But all the decisions of that officer have to be ratified
at a special biweekly meeting.
ARTHUR: Yes, I see.
DENNIS: By a simple majority in the case of purely internal affairs,--
ARTHUR: Be quiet!
DENNIS: --but by a two-thirds majority in the case of more--
ARTHUR: Be quiet! I order you to be quiet!
WOMAN: Order, eh -- who does he think he is?
ARTHUR: I am your king!
WOMAN: Well, I didn't vote for you.
ARTHUR: You don't vote for kings.
WOMAN: Well, 'ow did you become king then?
ARTHUR: The Lady of the Lake,
[angels sing]
her arm clad in the purest shimmering samite, held aloft Excalibur
from the bosom of the water signifying by Divine Providence that I,
Arthur, was to carry Excalibur.
[singing stops]
That is why I am your king!
DENNIS: Listen -- strange women lying in ponds distributing swords
is no basis for a system of government. Supreme executive power
derives from a mandate from the masses, not from some farcical
aquatic ceremony.
ARTHUR: Be quiet!
DENNIS: Well you can't expect to wield supreme executive power
just 'cause some watery tart threw a sword at you!
ARTHUR: Shut up!
DENNIS: I mean, if I went around sayin' I was an empereror just
because some moistened bint had lobbed a scimitar at me they'd
put me away!
ARTHUR: Shut up! Will you shut up!
DENNIS: Ah, now we see the violence inherent in the system.
ARTHUR: Shut up!
DENNIS: Oh! Come and see the violence inherent in the system!
HELP! HELP! I'm being repressed!
ARTHUR: Bloody peasant!
DENNIS: Oh, what a give away. Did you hear that, did you hear that,
eh? That's what I'm on about -- did you see him repressing me,
you saw it didn't you?
