Swift and Cocoa are like The Odd Couple. Two people, with drastically different personalities who are joined by fate to live with each other.
The Odd Couple Theme Song
One prefers things very explicit and will check and double check things are in order before starting a task. The other is happy letting things happen haphazardly, as things flow; the details can be worked out later.
One would only ever allow a single item type like socks in his drawer. The other is happy to store a mix of things in his.
One is very cautious with things handed to it, slowly unwrapping them. The other is extremely trusting and uses stuff passed to it without question, result be dammed.