Tells the listener not to do an action; 請 in front bows the command into a polite request.
框 · Frame
（請）別 [verb (phrase)]！
觸 · Trigger
You want the listener to hold off or not do an action, casually with 別 or softened with 請別.
序 · The move
1name the action to cut offis a verb following, not a thing being refused?
2set 別 in front of that verbis this aimed at the listener, not at stating your own plan?
3add 請 in front for a polite request, or leave it off for a casual onedoes the cut land on the action you mean to stop?
例 · Examples
1下了飛機以後after getting off the plane，別don't (cuts the action off)忘了forget打個電話make a call。
After you get off the plane, don't forget to give me a call.
界 · Boundary
不要
別 is 不要 fused into one fast syllable — casual, blunter (別走). （請）不要 is the full form, more able to carry weight and formality. Same command, register split.
別 + verb tells the listener not to act (別去 — don't go); plain 不 + verb only states a will is absent (不去 — I won't go). One halts another's deed, the other declines your own.
object after 別 for a command: 別話 → 別說話（別 cuts off a verb, not a noun）
negating your own plan as a command: 我別去 used to mean 'I won't go' → 我不去
請 placed after 別: 別請走 → 請別走（請 bows in front of the whole command）
English 'don't' is one word for every register; learners reach for 不要 where the casual 別 fits, or read 別 as its other senses ('other' / 'part') instead of the command.