The only one of those that makes sense is the last one. You've never gone for a walk and gotten tired?
No. I plan my hikes per my stamina and motivation for that day. If I want a leisurely 5-mile hike, I'm not gonna choose a 15-mile, high- altitude trail. But once I go on the leisurely 5-mile hike, I'm gonna complete it.
You've never been full and stopped eating?
Whether it's at the restaurant, or I end up taking some of it home, I still finish the entire meal at some point.
Just because a development team came up with more things than a player has time or inclination to do doesn't mean that players are bound to go through that content.
That's often the case with extra content (especially in an open world game), but this conversation is specifically about just the main campaign.
Forcing ones self to keep playing after a game's fun has worn off would leave most people with a worse experience in the end than a better one if they stopped enjoying the game and became tired of it.
If you're having fun with the game, then by definition you're not forcing yourself.
Playing to the extent that you can have fun with a game is the more effective way to enjoy it.
I've never picked up a game and thought anything about fighting the last boss or doing whatever the last gameplay task is, and I don't think I'm unique in that.
Of course you're not unique in that; I wonder how many people fall into that category.
The only thing I care about when I buy a game is having fun with it. That is all I want out of a game, that is my only "goal."
Fair, and ultimately this is the only thing that matters. Do know that I'm just asking questions out of curiosity and I'm not prescribing how you -- or anyone for that matter -- should play video games.
Everybody's different in what they're trying to get out of video games:
(1) For some people, it's just play a bit, take in the world and the mechanics, then move on to the next game
(2) For some people, it's when the credits roll after the main campaign
(3) For some people, it's 100% task completion per the game's completion tracker
(4) For some people, it's getting the Platinum Trophy/all Achievements
(5) For some people, it's becoming a true master at the game and perform spectacular feats -- speedrun, play with certain challenges (e.g., no weapon upgrades, no power-ups in Mario, etc), max out all the party members in their RPG, etc.
For every game I've played, I've fallen into every category except #1. I always end up enjoying the game enough that at a minimum, I want to see the credits roll.