2000 Reasons why you lost on time

The first one that comes to mind is the 2018 US Open final round 44-year-old Bradley Cornelius had a fatal heart attack during the game.

Yep... here's article about this topic https://www.thechessdrum.net/blog/2019/08/04/playing-chess-to-death/

Hang on….. what?!!?!??!

tbf people usually resign in this case otb, but of course in online chess nobody knows why they stopped playing...

Can you please stop? This is not a place for mortuary buffs! I t s  f o r  c h e s s  p l a y e r s ! 

but chess players die too!   ''definitely intentional sacrifice''  + Come what may = a hope for epic  revival to earn immortal status. that's how I roll...

Get lost 

It is one of the 2000 reasons a player may lose on time, including the one playing about 25 feet from the board I was playing on in that tournament almost four years ago.  If the title of the thread had been "2000 humorous reasons" rather than "2000 reasons" then it probably wouldn't have been mentioned.

If you want a moment of humor from that event then during the pause in play one teenage girl said to her opponent (almost 60 years old) "it is nice to see somebody so old still playing chess" (the opponent did not see himself as old and age prevailed over the 200 points higher-rated youth in that game).

You had booze the last night and you passed out in the middle of the game

You sat at the wrong (and unused) board number and found out with only moments left on the clock. I work a lot of tournaments and see people sitting incorrectly multiple times per year, though at least at the tournaments I work we generally check on all of the boards and figure it out before it becomes critical.  When it happens in a blitz tournament then there is rarely enough time to recover from the seating error.

You sat at the wrong board in the wrong section and took the seat of a person who was late.  When the correct opponent finally arrives, finds you in his seat, and gets things corrected, you've lost over 80% of your time and lose in the time pressure. 

This usually happens when the Sunday rounds start an hour earlier than the Saturday rounds and the person who was late was under the impression that there was no starting time difference.

PS The person who was late also lost about 80% of the clock's time as well and has the same likelihood to lose on time.

You are new to in-person tournament games and didn't realize that you have to physically press the chess clock after making a move.

In the evening round of a tournament you step outside the park district building to smoke and the door locks behind you.  It is distant from the tournament room and your knocking is not heard so you have to wait until somebody else leaves after finishing a game and by then you have little or no time left.

PS I have been a tournament director/arbiter since well before 2000 and am only listing things that have actually happened.  This last one is less likely to occur with cell phones being so common today but the strong tendency for phones to be silenced/turned-off during play means it still happens.

Everybody is allowed to hit their clock after moving (particularly important when there is increment). You are playing 3/2 blitz and moving so fast that between the time your opponent moves and hits the clock to start your time you have already moved and hit the clock (thinking you are starting your opponent's time but really the time is still running from the previous move).  Now your clock is running during your opponents move (you should hit it now to correct things but you don't realize what happened).  When your opponent finally moves you move quickly and stop your clock (from the previous move) while starting your opponent's clock for the current move just before your opponent finally hits to clock to stop his clock for the current move and start yours for the current move you've already made.  Now it is again your opponent's move while your clock is running.

You've moved so quickly that you end up having your clock be the one running most of the time.

You forgot to press the clock when you had a mate in 1

Or ... you didn't bother pressing the clock after you played checkmate and it turns out it was only check, not checkmate.  I've seen it happen a few times.

It happened to someone I know once once

?

You got a text message saying it was urgent found it was a prank and you forfeit on time