On my flight from Sydney to Heathrow I had a stopover in Bangkok. As I was going thru the gate to get back on the plane, the machine that reads your ticket made a funny beep, the lady pulled the ticket out, checked the screen and asked me to stand to one side. She then tapped away on her computer, wrote on my ticket, and said “I'm very sorry sir, but your business class seat has been allocated to someone else. I'm sorry, but we've had to reseat you in first class.� I said “OK. That's alright. Thank you. It's really OK.�.
First class rocks – it was like a 12 hour flight, so being able to lie flat, wearing 1st class pyjamas, with a duvet on the plane was really fun. The food is better than business class, with more selection. The chocolates are nicer too.
So, that's why seat 4K is better than seat 61A :-)