Came here thinking about how much my time as a B|X ref has helped me socially/professionally.
The 'B/X' edition of the game came after the "Holmes" boxed set,first published in 1977 and edited by J. Eric Holmes, and before the BECMI (Basic, Expert, Companion, Masters, Immortals) published in 1983 and later (and eventually compiled in the D&D Rules Cyclopedia published in the early '90s). They existed at the same time as Advanced Dungeons & Dragons, which had more, and more complex, rules.
Which part was difficult to grok?