Why do people lie?

I know this question is asked every time one finds out, without a shadow of a doubt, that someone has outright lied.
Have you ever asked somebody if they got your email and they replied that they didn't, even though you know they did bcause you have an email server, like at a university, where the email comes back marked as 'read'.
I'm not trying to be cynical here. I'm genuinely wondering why people lie I'm not saying I never lie either. However, I could never lie about not receiving someone's email or not receiving a package when I actually did receive it.
In addition, can one expect to have a truthful and honest relationship with someone who lies over such minor things
What do you think and what is your way of handling this situation

The verbal communication, the words we say, is only a tiny part of the human communication. When we talk to each other we communicate much more than just words and you intuitively know and use this. Even words we say are often not to be interpreted literally.

For example, if someone has stated that he had not read your email, although you know he had, the person might have thought something like "I do not want to talk about your email " or "I could not be bothered to do you the favor you asked in the email". Direct communication of such a thought may harm you or cause further unwanted questions.

Do not be that demanding about honesty; do not judge other people for being dishonest. Take it easy.

They have Fear to be honest. They believe when they tell the truth you wonA t like them anymore, or something bad is gonna happen- the are escaping from negative emotions.
I would suggest you believe the first one.
And often people lie because they donA t want to hurt you.

I lie because I don't want to hurt someone else or I'm afraid of the consequences of the truth.