To compare two scenarios:
Scenario one
[Context: One of the Chronicle Tenets is "Thou shalt not harm the innocent". One of the PC's Convictions is "Do what it takes to survive". Breaking a Tenet can incur Stains, breaking a Conviction can incur Stains or result in it needing to be changed/replaced, damaging a touchstone can incur Stains.]
The PC in question has, of their own volition, revealed to one of their mortal Touchstones that they are a vampire. This a breach of the First Tradition:
Thou shall not reveal thy true nature to those not of the Blood. Doing such shall renounce thy claims of Blood.
Through whatever series of events has led to this point, the Sheriff has discovered this Masquerade breach and is dutybound to rectify it. Logically, they
could just kill the Touchstone, drag the PC before the Prince for judgement and be done with it - a reasonable enough approach in setting - but I, as the GM, see the potential for more given the Convictions and Chronicle Tenets, so I figure the Sheriff will decided to make a point (all Kindred are sociopaths in their own way): they "ask" for the PC to meet them somewhere secluded, where the Sheriff is waiting with the Touchstone in tow, and upon the PC's arrival, demand that the PC kills their own Touchstone. This puts the PC in a bind: they can refuse - maintaining the Tenet but breaking their Conviction - and risking the Sheriff killing the Touchstone anyway; or they can acquiesce - breaking the Tenet (incurring 2 stains for a horrific act, reduced to 1 due to the mitigating circumstances of being forced), damaging the Touchstone (incurring a further 3 stains), but serving their Conviction (reducing the stains by 1). Of course, the PC can always
take a third option, like having their coterie mates sneak around and jump the Sheriff leading to further problems, or whatever.
Scenario two
The Nosferatu PC decides they want to spy on the Tremere Primogen and I improvise something about them meeting with the Toreador Seneschal to plot to replace the Prince. They can, of course, do what they will with this, but none of it relates to their Convictions or Tenets.
The first scenario was specifically designed to put both the Chronicle Tenet and Conviction to the test at once (often, it will only be one or the other), while the second had no such intention behind it, improvised in reaction to the player's declaration. Your post seems to suggest that pemerton would view the first as player-driven and the second as GM-driven (I know you cannot speak for them, so hopefully
@pemerton will clarify); whereas I view the first scenario as GM-driven, player/character-centred, and the second as player-driven, but GM-created.