I did that with FF7. I knew I could go challenge sephiroth for the last fight but I also knew that there were still a ton of secrets like summons and materia, plus the harder mode if I maxed levels. But I didn't get around to much of it and never beat the game.

And FF2 (snes) I made it to the final boss once, died to him, saw how far back the last save was, decided I didn't want to go through all that just to get back to the boss and instead returned the game to the friend I had borrowed it from, deciding I was close enough.

Mario Bros 3, I could only ever beat the game if I used a cloud to skip that last fortress before the final level select screen. It was a maze level iirc and I just didn't have the patience to figure out the correct path.