Poker as we all argue and rightly so is a very psychological game. By psychological, I don't mean the whole psychological warfare crap we keep telling others to make them believe we are in a very intellectual profession. I mean those psychological changes which happen to a player when he plays the game.
My previous profession had me research a lot on human psychology and I think it also gives me some insight into the psyche of a poker player. For example, you have a great day at the table when you crushed it for a bunch of cash and you feel like you are ready to go and take on the world elites! On other days when you get crushed, you feel like going into a hole and never coming out of it. Some even start thinking of the reason why they started playing poker in the first place.
If you are an emotional person in general, you are, in a way, prone to this happening to you. You can prevent it only by being very aware of your surroundings or situations which will be a task when it happens. They call it rage, we call it tilt. Think about it. There is no other profession in the world (Stock trading might be an exception) where a bad day at work would mean you are down a portion of your net worth. That's a huge burden for anyone.
I remember railing one of my very good friends and one of India's best players in a high stakes cash game a couple of years ago. In this hand, he gets it in with AA pre-flop and for a high seven-figure pot and I saw his hand literally shiver. I am talking even after the pot. This player is probably India's best Holdem/Omaha player and this happened to him and he is one of the most level-headed people I know. Now put yourself in his shoes and think what would happen if you were in his spot.
In short, Poker = Joy + Fear + Excitement + Anxiety + Depression + Elation all put in one.
Think of what happens to a human mind when it faces this kind of abuse daily. Most of this can be solved with one simple solution. Bankroll Management. This is one key element which makes the psychology of poker manageable for most people. If you are feeling pressured playing 50-100 or 100-200 and failing to make correct decisions because of the stakes, drop down without fear. Because you win rate, profitability and happiness EV will be way higher.
Else you will always have a love-hate relation with poker.