RAW 1E life for a MU was brutal and often very, very short. You started with 4 spells (IIRC) in your spellbook, three chosen by either dice or the DM, and had to choose exactly which one you wanted each day. This joy lasted until you got more experience than any other PHB class required (except Paladin?), then you got to prepare TWO of them! This assumes you didn't die a horrible death first, which was not only common for all 1E characters, but you also had the lowest HD too. IME most parties had one of two views on low level MU's: "keep them around, because they'll be amazingly useful some day" or "I push the MU at the monster and run."