Vaas Montenegro delivers the game’s most quoted monologue — ‘Did I ever tell you the definition of insanity?’ — in the opening section of Far Cry 3. The speech, about doing the same thing repeatedly and expecting different results, is presented as the villain’s characterisation. It is also, structurally, a description of the game’s mechanics.
Far Cry 3 is a game where the player raids outposts, which respawn, requiring the player to raid them again. The hunting, the crafting, the liberation loop — all repeating cycles where the same actions produce the same results. Vaas’s definition of insanity describes the player’s activity with more accuracy than his own behaviour.
Michael Mando’s performance improvised significant portions of Vaas’s dialogue, including variations on the insanity speech that were not in the original script. The recorded takes that were not used have never been released but were referenced in subsequent interviews as equally strong. Vaas became the most discussed Ubisoft villain in years on the strength of Mando’s physical performance in a character role that was originally a secondary antagonist.
The game’s decision to kill Vaas at its midpoint, while he is the most compelling character and Hoyt is demonstrably less interesting, was the subject of criticism at release and was cited by the development team as a deliberate choice — the game needed to lose its best villain to demonstrate that the protagonist had stopped being a victim. Whether this trade was worth it remains contested.

This is exactly why I love this game. So many layers underneath the surface if you just take the time to look.
Stumbled across this on a late-night session and couldn’t believe it. Your explanation finally made it click.