Law of Diminishing Returns

I was discussing with my roommate about Economics (theoretical) and how its laws help us to take rational decision in life. Then he told me about the Law of Diminishing Returns.

As per Wikipedia "According to Law of Diminishing Returns, in a production system with fixed and variable inputs (e.g. factory size and labor), beyond some point, each additional unit yields less and less output."

This is an universal law. It applies perfectly to various aspects of life. Take a example of learning curve.

In learning a new language an individual may reach a point at which studying that language with the same effort for the same amount of time will no longer provide the same increase in comprehension as it had it in past.

Now I will try to make it more realistic with this example.

Lets say you have a dog and you feed him with 2 breads daily. Both breads are identical, made of same material and of same size. But the response dog gives for second bread will always be less than the response of having the first bread.

It's a very basic example but helps to understand many things around us.