When the first bad beat of session pisses you off and puts you in a negative mindset that affects your game. If there are more of them - you already can't control yourself and fall into loser /unfair mindset. You definitely should not continue and take a good break from poker.
Also when you play for a few hours in MTT and you don't feel excited/ anticipate a good result / is motivated to play your best, but instead you feel already tired and subconsciously want to bust because you either had enough already or you find other things to be more fascinating than poker at the moment.
Yes, in both these cases a player should have checked himself before the session and if he realized that he is not a 100% prepared for a session, then he should not start it. But if he has started and feels like I've stated above, then it's important to take this mental state seriously and don't push it the next day, or whenever you next session was planned. In my opinion, forget about poker until you will feel pumped up just while thinking of it, and then return fresh, confident and ready to deal with whatever will happen in a session.
__________________
|