I reckon if you earn so much money (is Unai on about £8m a year with us?) that if you then get an offer of, say, £12m a year it is almost inconsequential. What are you gonna do with that extra £4m minus applicable taxes that will improve your standard of live so much that it'll be worth it?
You're already easily able to eat in the best/most expensive restaurants, have the most expensive accessories, the nicest cars, fly business class to anywhere on the planet on your time off. You've probably already got a pile of stocks and shares and cash, probably a load set aside for the kids as well.
Throw in that if to get that extra £4m you have to relinquish certain controls at your new destination, trade decision making and influence, as well as uprooting your nearest and dearest and you know you're already on to a good thing, then is it worth it?