Deception

How well do you know anybody. Pick somebody, decide for yourself. How well do you reallllly know the inner workings of a person? Try to decide about your spouse. Your neighbor. Your sibling. A coworker.
The fact is, you know your friends and acquaintances in much the same way that science has been developed. Evidence.
I remember my seventh grade science class perhaps better than any other science class. The whole year was spent towards the final exam; which is not unusual at all. In this class, however, we were to be given a test tube of miscellaneous stuff and the test was based on how well we experimented to determine what the stuff was made of.
We used every bit of the chemical science that we had been taught and had experimented with through the year. density, color, odor, flammability, interactions with other chemicals, you get the idea.
I hate to be the bearer of bad news, but this is much the same way that you know the hearts of those around you. None of us has a magic truth serum. We cant read minds. And so we are relegated to that seventh grade device of observing the evidence. The best definition of deception is to me the picture of reality going against the evidence.
When your best friend wrongs you in some way. A close business partner turns out to be stealing from you. Your spouse cheats. You can feel free to add examples of your own.
All conversations regarding the situation seem to include the words "you never would have thought" or "nobody could have imagined."
When it is plainly seen that somebody is not on your side, there is no deception. It does not surprise you when your competition tries to eat your lunch. You are not surprised when your enemy tries to hurt you.
But when you have entrusted somebody with something, based on the evidence, and the evidence turns out to have been false, it always comes as a shock.
Oddly, and what is a bit fascinating, is the fact that the only way our evidence is usually proven wrong is through the examination of new evidence. The world was flat until evidence to the contrary came to light. Your secretary was trustworthy until you found records to indicate they were stealing. your friend was true and blue until you heard what he said behind your back. It never fails that evidence is true until its falseness becomes evident.
This is by the way how innocent people go to jail. Not enough evidence. Think about being framed for something. Those framing you would allow only so much evidence to come to light as it takes for a conviction. Any more and you might be proven innocent.
In short, be sure to examine and find all of the evidence before you decide that you aren't being deceived. you might be surprised at the true intentions of those you trust.