For me, and many others I am sure, the real precious commodity that we never have enough of is time. You cannot make more time. You can waste it or manage it well but ultimately it is a fleeting finite item in our lives that passes far too quickly and generally without our permission. I know I have a tendency to exacerbate this issue by taking on more things than I can fit into any normal schedule but I have so many interests that I struggle to turn down any of the events or projects that are mentioned to me.
Many writers I know also deal with the A.D.H.D. issue of having so many ideas in their heads that we have to constantly take notes because we can only work on a few things at a time yet our minds are bombarded almost constantly so we have to be prepared to step out of one setting and into another with a new group of characters for a quick side note then right back to the original piece. By the time we get finished with part one and move on it can be hours, days or even moths later. We never seem to have enough time to get to everything on our to do lists, partially because we always are adding to them.
Time management may be key to being productive however no matter how much I manage it I still find that I run out. I make my priorities, sleep generally gets the short end of the stick on that one, and I jump from project to project in order to try and accomplish as much as possible. People tell me that burning the candle at both ends will cause me to fizzle out too soon someday and they are probably right but until we invent a way to create more time or I get a clone I will keep pushing as though tomorrow will never come.