An additional comment (at least from my experience)
A roll of 20 on a d20 does always hit, no matter your THACO or your opponents AC. Also, a roll of 1 on a d20 always misses, again no matter the circumstances. In addition with a roll of 1, you not only miss, you also have a chance (albeit a small one
) of a 'mishap', like damaging yourself, someone in your party, dropping your weapon.......
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Ever wonder if illiterate people get the full effect from alphabet soup?