That isn't obvious at all. Folks get smitten by people they've barely met. It doesn't take years to be tricked into joining a cult: You can convince folks in a matter of months.

John might be 10 years into your lies, but he also might have caught on. You use different lies with Jane, who might not know better, and she listens wholeheartedly and with good faith.

If John is an adult and Jane isn't, Jane is easier even with the age difference. This is simply because of lack of knowledge and experience.

If one has more access to the outside world than the other, they are less likely to believe your lies.

If John knows you have mental health problems that causes you to lie and Jane doesn't, Jane is easier to lie to.

Maybe John is more suspicious of people and the world. Maybe John just shuts up to appease you, like folks that avoid talking politics with their families simply don't want to deal with things.

Are you someone younger? DO you have authority over them?

There are so many things that affect whether or not you can lie to someone.

You hear something from someone who's been talking to you for 10 years, and from someone you've just met. Whose lie is easier to detect?

Here is an even better way to phrase the question with respect to schooling:

You spend 10 years telling John and Jane some stuff every day for hours. John also gets told stuff for hours by a third party while Jane gets all information from you. Which one is easier to lie to?

School adds a third party so that the child isn't reliant on things taught by their parents.

It is interesting because for me it was obvious that Jane will be the easiest to lie to by far. John knows you much better.

Usually psychopaths and sociopaths are always moving so people don't know who they are and they can fool them easily.

What you are saying is if someone does trust you, you can lie to her easier, which is true, but then you will loose the trust and bond that took a long time to get.