The first time a balance has a comma in it, it reads as somebody else's — a clerical error you're waiting to have corrected.
Handling large amounts turns out to be less about arithmetic than about nerve. Not panicking. Not making a fast decision because a number is making you nervous. Sitting with it for a fortnight while nothing happens.
People who move real money are mostly unhurried. The skill on display is patience wearing a suit.
Whatever you're holding right now, you're already practising on it.