Given Heathrow's third runway was the most controversial of the three expansion options on the table, given it's the most expensive, given it will take the longest to build, is the most politically risky, has Conservative opposition, has already forced a concession on Cabinet collective responsibility, given Boris doesn't like it (I could go on ...) you do have to ask why Theresa May has decided to green light this particular scheme.
It's because this decision isn't about capacity alone.
Gatwick could provide extra planes for the crowded skies of the south east.
The other option - a longer runway at Heathrow - could also enable more planes to take off and land.
But it's because the decision to expand what is already Britain's biggest airport is closely to tied to the UK's exit from the European Union.
Britain, right now, needs to stick up a very big sign saying it remains "open for business".
And you might recall the mantra of the Brexiteers both before and after the referendum was about connecting the UK to new trading partners around the world.
Heathrow, the Government believes, represents the best way to do that.
Firstly, business travellers want a hub airport. And that means the UK must compete with Charles de Gaulle airport in Paris, or Frankfurt in Germany or Amsterdam's Schiphol airport.
A hub gives those business travellers an airport in which to change flights and connect to another part of the world.
They don't want to offload their bags into a coach and travel round to Gatwick to pick up a flight to their destination of choice.
They will decide to take flights through Paris or Amsterdam instead.
Secondly, Heathrow currently has very poor connections with other regional airports in Britain.
That means travellers can't get from their local UK airport to their final destination via London. And again are likely to chose other hub airports outside the UK.
It's why many regions of the country, including the Scottish government, support the third runway at Heathrow.
The west London airport is also more accessible by train and car (and soon HS2) to Wales, the Midlands and the North than Gatwick (which sits to the south of London).
And these are the same reasons why the three-year-long independent Airports Commission concluded Heathrow was the best choice.
But it reported nearly 18 months ago - and still the government hasn't acted until today.
So far so (fairly) obvious.
But as I mentioned at the outset - Heathrow is facing huge challenges.
Politically, Boris Johnson and Justine Greening are two prominent members of the Cabinet who oppose Heathrow and will continue to do so.
Environmentally, Heathrow affects many more people in terms of noise pollution and air quality challenges.
Legally, there will be many challenges and obstacles.
But the message Theresa May wants to send out loud and clear today is that Britain is 'open for business' in this post-Brexit world.
And so that is why they opted for the toughest decision: Heathrow.