You have something in common with people who fall behind on their bills, argue Harvard economist Sendhil Mullainathan and Princeton psychologist Eldar Shafir in their book Scarcity: Why Having Too Little Means So Much. The resemblance, they write, is clear.

Missed deadlines are a lot like over-due bills. Double-booked meetings (committing time you do not have) are a lot like bounced checks (spending money you do not have). The busier you are, the greater the need to say no. The more indebted you are, the greater the need to not buy. Plans to escape sound reasonable but prove hard to implement. They require constant vigilance — about what to buy or what to agree to do. When vigilance flags — the slightest temptation in time or in money — you sink deeper. 

Some people end up sinking further into debt. Others with more commitments. The resemblance is striking.

We normally think of time management and money management as distinct problems. The consequences of failing are different: Bad time management leads to embarrassment or poor job performance; bad money management leads to fees or eviction. The cultural contexts are different: Falling behind and missing a deadline means one thing to a busy professional; falling behind and missing a debt payment means something else to an urban low-wage worker. 

What's common between these situations? Scarcity. "By scarcity," they write, "we mean having less than you feel you need."

So a key to life is saying NO -- and this is one of the lessons of Adam Grant's "Give and Take", too.

Being organized helps, too, but NO is still the most important word to learn how to say.

"Scarcity captures the mind," Mullainathan and Shafir write. Starving people have food on their mind to the point of irrationality. But we all act this way when we experience scarcity. "The mind," they write, "orients automatically, powerfully, toward unfulfilled needs."

Scarcity is like oxygen. When you don't need it, you don't notice it. When you do need it, however, it's all you notice.

For the hungry, that need is food. For the busy it might be a project that needs to be finished. For the cash-strapped it might be this month's rent payment; for the lonely, a lack of companionship. Scarcity is more than just the displeasure of having very little. It changes how we think. It imposes itself on our minds.

And when scarcity is taking up your mental cycles and putting your attention on what you lack, you can't attend to other things. How, for instance, can you learn?

When we are young, we have plenty of time and space in our minds to learn. We're like sponges.

Once we're older, that time and space is occupied so we have to MAKE time and space.

It's not something that happens by default. It's something that we need to work at.

Put another way: getting older means choosing between tradeoffs.