In the US "Flying" magazine they have a column by Les Abend who flies 777 internationally and internally for one of the big US airlines - about a third of his articles make reference to issues about fuel and diversions (planned, actual, possible)
The system is pretty full of 'planes, the problems with long taxying waits, changes in routing due to sudden changes in weather, sudden problems in weather at destinations all play hob with any planning schedule
You just have to accept that occasionally your captain will decide to play it safe and go and top up before he has to declare an emergency or worse.....