Suppose we take a simple logical argument that A implies B. This means that not A implies not B. A simple case could be that if it is raining then that implies that it is cloudy. Therefore, if it is not raining then that implies that it is not cloudy. No confusion there, seems to make perfect sense. Let's now say that if you have a crow, that implies that it is black. All ravens are black.
Therefore:
All nonblack birds are not ravens
What if however we see some other creature, say a bluejay. A bluejay is neither a crow nor is it black. We could then say that this satisfies our statement that all nonblack birds are not ravens. We are seemingly reinforcing our concept of ravens being black by saying that a bluejay is not black. Obviously, bluejays are blue.
However, what if then we see a red cardinal? This is also reinforcing a statement that all nonred birds are not ravens. The red (nonblue) bird is a cardinal (not raven).
This leads to the statement:
All ravens are blue
Obviously there is a problem with this! This shows that there is a fault in our system of logic. Can you see what it is? This is known as the ravens paradox.