Besieging a moated castle is really hard. I mean really, really hard.
Here’s a list of things you can’t do with a moated castle:
And here’s some things that are really hard to do with moated castles:
And here’s the list of things you could do:
In reality, prior to the invention of muskets and cannon, which really rendered castles obsolete, moated castles were really hard to take.
Caerlaverock Castle in Scotland is a moated castle that fell a few times, most notably in 1300 when Edward I besieged it with a force of more than 3000. The castle was held by a mere 60 Scots, and the castle was taken when the defenders surrendered, apparently overcome by exhaustion and wounds.