Hot big fuel injected engines - a delight!
The fuel lines across the top of the engines get hot and turn the cool fuel remaining in them into hot vapour. This will ignite more easily so you leave it alone to get on with the job and don't add fuel until it fires.
Failure to do this causes more cool fuel through the pipes, flooding the engine with too much fuel before it gets a chance to ignite.
It's probably more complex than that - but that's the idea behind it and it works everytime.