beginners most common problem

Thanks...

There's a few there that I definitely need to work on myself. 

Losing.

I'm not even going to try bullet/blitz.

Undefending a defended piece   or pawnand both leaving a piece under attack and moving a piece into attack.

- Leaving unprotected pieces unprotected - Not noticing unprotected pieces on opponents side - Making empty threats - Trading pieces just because they can too often

I'd also add: ignoring king safety

opening lines that should be closed and closing lines that need to be opened.  Actually, I do not see that as a problem for beginners because most players do not understand lines till they reach 1700.  Beginners need to stop hanging pieces and stop a mate in one.

"Hoping for opponents to blunder as many pieces as they can so that he/she can win"

Promoting all the surviving pawns to queens and accidentally stalemating the opponent.

Yeah, we all did that when we were beginners.  When I got stronger, I used to panic when my opponent made a break. Lol.

https://www.chess.com/article/view/the-10-most-common-mistakes-among-chess-beginners

https://www.chess.com/article/view/the-64-commandments

That's pretty good, but "playing without a plan" is something you can't avoid for a long time, so I don't think it belongs on a list of common beginner mistakes.

For example, hanging pieces can be overcome through sheer will power, but having a plan in most positions requires years of experience.

One thing about chess is it takes quite a bit of skill to know when to beak a chess principle. So beginners have to follow basic opening principles in order to get a playable middle game.

Mariners.  I do not think a beginner can stop hanging pieces through sheer wild power.  It takes training.

I was just going to ask - how on earth do you work out which lines are which - but I'll wait till I'm a LOT closer to 1700

Basically, when you attack you want lines open.  When you defend, you want lines closed.

F pawn.