"I could have been a contender" on the darts stage if I'd been any good at maths. It always amazes me at how these professional players, who are hardly rocket scientists, are so good at adding up and can work out their finishes almost instantly in their heads with all that pressure. I'd be standing there for five minutes trying to add on my fingers.
They don't work them out, they learn them.
Throw after throw after throw, they are constantly going for the same finish combinations in hours and hours and hours of practise.
It's repetition that does it.
You only have to see their confused little faces on stage when they sometimes miss a big number or land in the wrong treble.
Most of them are completely incapable of recalculating, so they ask the referee what they have left.