(Not counting MGR) the only Metal Gear game I've played was Portable and Metal Gear Solid for PS1 when I was 7-9.
Other than that...I've mostly experienced Metal Gear through fan animations and mentions from LPs.
The issue is that if I forget up even once in the slightest way, I just rage quit and restart from the last point where I was. If it becomes too much of a problem, I just drop the game for months, even years until I feel like taking on what ever challenge was halting my progress.