There were a lot of things working against you as a high level caster in AD&D. It wasn't uncommon to fight an enemy with an immunity to some effect. Magic Resistance was handed out like candy, even to some fairly weak enemies. Stronger enemies got very good saving throws. Big spells took more segments/had a higher speed factor and so the chances of someone getting to deal damage to you and make you lose the spell were high.
A lot of DM's I played under were just unfriendly towards spellcasters as well. Every spell was went over with a fine-toothed comb. If the DM made a ruling on a spell that nerfed it or made it useless, you had no recourse. That was how the spell was and writing in to Sage Advice was far from guaranteed to get you an answer (and definitely not a timely one), plus, even then, you had people who just said "Sage Advice is wrong", lol.
Like I joined a game once where the DM had it in his head that the spell description of the Magic Missile spell (Area of Effect: 1 or more creatures in a 10' cube) meant that each Missile did damage to everyone within 10' of it, so my attempts to use it instantly caused friendly fire! Nothing I said could get him to back down either, so I just had to stop using the spell in a lot of combats!
Enemies might have magic gear specifically designed to protect against your spells, as if things weren't rough enough "Oh, well of course the Orc Boss has a Ring of Fire Resistance/Protection +3/Spell Turning". Dead and Wild Magic zones appeared without warning. Spell Mishap tables were cobbled together. Your spellbooks and material components were always being targeted (my favorite was "it's raining so your material components get wet and you can't cast Fireball").
Actually getting the spells you wanted was fun too- Gary came out and said you should never do it, and even in 2e, you would often have to roll randomly to get new spells...and there was always that chance you failed to learn them. Oh and if you were a specialist? Funny how your enemies would always stock spells you couldn't cast!
And I know that for everyone who reads this and goes "Come on, James, there's no way that actually happened", there's going to be one person who will think "ah, the good old days."