The entropy can be interpreted as a measure of disorder, but we will especially see an increase in entropy means a waste of energy. 

Imagine a trolley at the top of a slope. Imagine that on wheels, we will install a dynamo bicycle, which charge a battery. The dynamo will take the kinetic energy to the trolley when it will set in motion, and therefore the brake. To those, I hope many who have already used a dynamo on a bicycle, you know that is more difficult to move when it works is simply that energy you spend does not just put you in motion, but also to turn the dynamo, which produces electricity. If we charge a battery to the dynamo, at the end of the experiment, the trolley will also be moving down the slope, but all its potential energy has been dissipated. A portion was converted into electricity by dynamo, and stored in the battery. 

In fact, if the battery has managed to recover all of the potential energy, the entropy of the system did not increase, because energy is always tidy. It is simply stored in the battery now. So if no energy was lost in the form of thermal agitation, disorder has not increased. 

If we had not put battery, disorder would have been much greater. We have squandered all the potential energy in the form of thermal agitation. The increase in the disorder would have been possible. 

What is happening in practice, an intermediate situation. Some of the initial potential energy of the truck is recovered in the battery, the other is wasted. The increase in the disorder is not zero, but it is not possible. 

For against, one thing is not possible: that the thermal agitation, which is a lot of energy still got to put the cart in motion, voluntarily, even small movements. This charge the battery, and would mean we have managed to recover thermal energy from the rails. Decreased disorder. Maybe we can slow the increase in the disorder by recovering energy, but not to reduce the disorder. It is forbidden by the second principle! 

We therefore concluded that 

Anywhere a spontaneous evolution of a system is possible (where an increase of entropy is possible) this means that energy can be recovered. 

An increase of entropy is a waste of energy. 

Wasted energy is irreversible. The wasted energy can be recovered, this would contradict the second principle.