Rules You Didn't Know

[Reynard]

So today I learned that moving through allies in 5E is difficult terrain. I have been playing and running 5E since it was released and I have never known, let alone used, that rule. Huh.

So, what game rules did you have no idea about until you happened upon them by chance? How long were you playing the game "wrong"? Did you incorporate the missing or misunderstood rule? Did you keep playing the way you had been?

 

[Alzrius]

A while back, I stumbled upon a passage in the PF1 Core Rulebook that explicitly stated that when a critical hit is scored, you actually roll the damage die multiple times, rather than just multiplying it; apparently, the "x2" or "x3" in the weapon tables were just shorthand, but we'd actually been rolling the die once, adding the modifiers, and then multiplying it accordingly, for quite a few years.

When I pointed this out to my group, we all decided to keep doing it the way we always had.

 

[Irlo]

In D&D 5e, casters lose concentration when they’re paralyzed. We started using the rule when we noticed it, but it took years to notice it.

 

[Wolfpack48]

I'm just gonna put own our very first eureka moment when we first started playing AD&D back in 1977. Hit DICE are not the same as Hit POINTS, and you use Hit Dice to determine how many Hit Points the monster has. We were all wondering why Dragons were so easy to kill, but when we made this discovery, it was an amazing and happy day.