"Yackum," aka "rambling," aka "unnecessary nonsense," becomes the vice of all writers when slogging through draft 1 of an unpublished short story. Novelists can get away with yackum, especially if they are literary elephants like Stephen King or J.K. Rowling, but short story writers do not have that luxury. Unlike novelists, who experiment with their medium to the point of exasperating us readers, the short story writer has to tell a story. Period.
Types of yackum to look out for:
1) Dialogue- Usually worse in novels, but unnecessary or flat dialogue must go. If it sounds false? Cut it. If it has one word off and the word can't be removed? Cut it. Characters put the "yak" in "yackum".
2) Inner Dialogue- Even worse than outer dialogue because it occurs in the character's head. Aka Rambling for God Knows How Long, especially in a mystery. Show your character's reaction, don't have them say it. Yak in yackum, folks!
3) Description- Hairier than dialogue, but rely on your ear for this one. If you read at an open mic, you'll trim on the fly to avoid being cut off in the middle. You want concise and lyrical sentences. And if you have even one paragraph (four sentences) waxing on, the editor will probably slap your manuscript. Here you can break the dialogue rule and have other characters judge your protagonist, or each other, as long as you keep it concise and clear.