ask a busy person

J: Zach had two of his friends round for tea tonight, he was supposed to be going to their house after school but their mum said she couldn't have him after all and would have to cancel so I said her kids could come to me instead.
D: yeah I always end up having everyone else's kids too
J: I know you do. When I dropped them off home at nearly 7 o'clock it occurred to me that I'd been working all day 30 miles away and had been on the go constantly whereas their mum Julia doesn't work!
D: that's the same as Karen next door - I always end up feeding her kids when I get home from work even though she's home all day
J: Margie's dad, Norman, explained it to me at the weekend though. He said that if you want to get something done you should ask a busy person!
D: oh great! Why's that?
J: because if you've got a million things to do already, one more thing doesn't seem like much more, but if you've only got one thing to do, one more thing doubles your workload and seems insurmountable!