If I have a split verb, such as "pick up" and I am a addressing a third person, I can say either:
I will pick Fred up at 11am.
Or:
I will pick up Fred at 11am.
For the second person, we have:
I will pick you up at 11am.
But it sounds wrong if I say:
I will pick up you at 11am.
What is my missing understanding here?
UPDATE:
My understanding from reading the possible duplicate question and the given answers, is that there is no strict rule about this at all, only a matter of style.
Thinking about it, I realised there is nothing wrong with the fourth example above, for example, if you wanted to give emphasis. Imagine saying the sentence and pointing your finger at the intended person:
I will pick up you at 11am.
It is no longer an awkward sentence, but becomes a highly emphatic one.