Since it is a mode that depends quite a lot on “luck”, players in Teamfight Tactics sometimes find themselves in extremely frustrating situations, making it difficult to keep a “cool head” to calculate their next moves in the game.
Here are some of those annoying situations:
Encountering players with “infinite luck”

In Teamfight Tactics, sometimes you can arrange your pieces, pick counter items, and calculate every detail… but all that effort goes to waste if you encounter a player who is too lucky. For example, having Garen in round 2-1, or a 2-star Gangplank at level 7,… In such situations, many players often choose to continuously “Ping ?” on the enemy’s house to vent their frustration.
Getting “ks’d” by a very strong comp right from the start

Shredder Xayah is currently a relatively hot comp because it is easy to play and arrange, so it is chosen by quite a few players. However, even though Xayah is a 1-star champion, she can still be “ks’d” if everyone is trying to play Xayah. This situation leads to many players “dying together” because everyone insists on “sticking to the flow” and refuses to change their comp.
Situations of “having everything but missing you”

Many players refer to this situation as being “baited” because sometimes there are crucial champions that never appear on your board. For example, in the early rounds, you have a plethora of perfect champions for a Cybernetic setup like Leona, Fiora, Lucian, Graves, Vi, Ezreal,… and you decide to play this comp, but ironically, even after rolling at level 9, you still can’t get Ekko, leading to an incomplete comp and dropping out of the top 4 in helplessness because now it’s too late to pivot.
Items drop that are completely unrelated to your comp

Playing a comp where your pieces appear without needing to roll is an extremely comforting feeling, however, when each time you fight monsters, the items that drop are completely unrelated to your comp, it is an incredibly frustrating feeling. Just imagine playing a Mage setup and the monsters drop only BF Swords, or when playing a Brawler Gunner and Kayn drops a Dark Star Heart,… these are all extremely annoying experiences.
When you are “selling health” but encounter a stronger “health seller”

Many players often choose to arrange weak pieces to get a losing streak for money or items, however, sometimes you meet someone who shares the same strategy, and that person is even “selling health” stronger than you, forcing you to win and lose your losing streak.
When you need items but the monsters drop only “gold”

Each monster round gives you the chance to receive great items for your comp, or sometimes if you are playing Cybernetic, and any item would do to activate the passive for more strength. However, the result is that in a round with 6 monsters, only one piece of any item drops, while the rest are all gold, causing your main carry in the comp to not gain any power at all.
When you have Neeko but can’t use it

Because the rules of Teamfight Tactics only allow a certain number of champions to appear on the board. So sometimes you might have 2 2-star Jinx, 2 1-star Jinx and want to use Neeko immediately to get a 3-star Jinx.
However, the result is that there are already 4 1-star Jinx floating around on other players’ boards, so you can no longer use Neeko; you can only wait for those players to “drop out” or sell Jinx. This situation sometimes leads to unfair losses because you couldn’t upgrade your strongest carry to 3 stars.