The oldest versions of D&D did specify rolling 3d6 in order for STR, INT, WIS, etc., and then you would choose a race and class based on what you got. People did not like that! So then they tried adding a point-swap thing, where a mage could trade 2 points of DEX to pick up one point of INT, and so on. Then the Advanced D&D series came out (the big one), and they offered four methods at the DM's choice:
Method I:
All scores are recorded and arranged in the order the player desires. 4d6
are rolled, and the lowest die (or one of the lower) is discarded.
Method II:
All scores are recorded and arranged as in Method I. 3d6 are rolled 12
times and the highest 6 scores are retained.
Method III:
Scores rolled are according to each ability category, in order, STRENGTH,
INTELLIGENCE, WISDOM, DEXTERITY, CONSTITUTION, CHARISMA. 3d6 are
rolled 6 times for each ability, and the highest score in each category is re-
tained for that category.
Method IV:
3d6 are rolled sufficient times to generate the 6 ability scores, in order, for
12 characters, The player then selects the single set of scores which he or
she finds most desirable and these scores are noted on the character
record sheet
These methods allowed much more flexibility in choosing the player race and profession, and at the same time, getting an 18 in anything was still a special and rare thing. Then as you play through the levels, you encounter magic which can increase your scores, so for example by 15th level it was not that unusual for a character to have an 18 in their prime requisite and maybe some other high scores as well. And the thing is, those points were earned through adventure. Stat increases were prizes, not entitlements.
