Gygax stealing Arneson's idea.
Gygax butchering Arneson's idea.
Gygax moving from an open system meant for DIY at the table (OD&D) to a closed system meant to be played one true way (AD&D).
Arneson being fired from TSR.
Gygax screwing over Arneson in the royalties.
Arneson having to sue Gygax over royalties.
Arneson winning the legal battle against Gygax over royalties.
Tables not keeping strict time records.
Tables forgetting that D&D used to be run as a meat-space MMO with 50+ players at a time.
Table remembering that D&D used to be run as a meat-space MMO with 50+ players at a time.
AD&D Unearthed Arcana.
The switch from unarmored being AC9 to unarmored being AC10.
The switch from AC starting at 9-10 and going down to AC10 and going up.
Stats being presented in the wrong order. It's supposed to be STR, INT, WIS, DEX, CON, CHA.
The publication of Dark Sun.
Misprinting the price on that one Dark Sun book for 4E.
The refusal to publish Dark Sun for 5E.