不 un

as in, "Doing meth is FUcking unlucky, and really FUcking unwise. "

below (下) + one stroke. You can think of 不運 (unlucky) or 不平等 (unfair) as being below or less than lucky or fair.

mystery ★★★★★
不 (un) + 思 (think) + 議 (discussion) = 不思議 (mystery)

a mystery or unexplainable thing. BOOBOO:NOT a mystery like Sherlock Holmes or "Colonel Mustard, in the drawing room, with the double-headed dildo." A mystery like how fat Americans are, or why Sting is famous. That's a fushigi.

unease ★★★★☆
不 (un) + 安 (cheap / safe) = 不安 (unease)

inconvenient ★★★★☆
不 (un) + 便 (convenient　/ poop) = 不便 (inconvenient)

shortage of ★★★★☆ NP
不 (un) + 足 (foot/ be enough) = 不足 (shortage of)

To not have enough of a physical thing (money, time, nurses, teachers.) Also implies that there is a specific amount that is required, For example -犬不足 (a dog shortage). There's no particle or verb needed.

affair ★★☆☆☆
不 (un) + 倫 (principles) = 不倫 (affair)

an affair - cheating