Yoga is not a marginal activity in 2012.

WSJ: Yoga in the Olympics? Jason Gay Weighs In

If the marginal benefit of each activity decreases in the presence of the other activity, then chances are they aren't worth pursuing together.

WSJ: Finding an Innovation Strategy That Works

Investors have recently rushed headlong into treasuries for fear that the economic recovery could be vulnerable to signs that activity is facing a marginal slowdown.

FORBES: Long-Dated Bonds Hit Weakness Worldwide

In the same way, an increase in marginal tax rates leads to less domestic trade or economic activity.

FORBES: Why President Obama's Tax Hike Will Hurt the 98%

The marginal tax rate is the rate on the next dollar to be earned from any investment, enterprise or productive activity.

FORBES: The GOP Jobs Plan Vs. Obama's