How easy is it to live a lie.

You mean like, hiding a body in the back yard or cheating on a spouse yet still living with them and pretending fidelity?
I would think there would have to be a disconnect between emotions/empathy and the brain. Or they've justified it to their conscience and suppressed it...?

I think it probably would, if a whopper of a lie. I know I could not live a lie for any length of time. .....bit thick, me.

for me it would take extraordinary energy to lie and keep it going and remembering what i did

I should ask my brother how he does that 🤔

No, just good acting ability.

will power, usually the consequences help continue with confidence