How does the deception theory relate to our every day lives?
Since you have placed this in the business section, I will talk about the implications of deception theory for our everyday dealings in the business world.
For example, almost all of us have bosses and many of us have some sort of supervisory responsibility over other people. Deception theory can help us understand our interactions with such people. If we supervise others, deception theory helps us know how to try to determine when we are being deceived. It teaches us to look for things like leakages that tend to indicate that others are being deceptive. If we have to try to deceive our bosses (or our subordinates, for that matter) deception theory helps us to understand what sorts of things make it look like we are being deceptive.
In these ways, we can use deception theory to help us interact with our coworkers on a daily basis.