Ways to notice opponent's threats during one's own move I am currently playing in a tournament and my last game was a total disaster. Without going into details, I missed a two-move threat my opponent had in the position (I'd expect a ~1600 Elo rated player to find this threat during a game) straight out of the opening and my position was practically hopeless afterwards.

However, after some time spent on self-pity I started reflecting on the nature of my blunder and I started to realize that this is a type of blunder I've lost countless games to. In this game, the following happened:


I was having trouble finding a good plan out of the opening, and before making the losing blunder I spent around 30 minutes on the clock.
The move I played should have been easily recognizable as a blunder for a player of my strength (~2200 Elo at the moment).
I noticed the threat almost immediately after pressing the clock, long before my opponent actually played the winning move (naturally he was a bit suspicious that someone like me would miss something THAT obvious; I could even see him throwing some suspicious glances, seeming like he wanted to ask me: "Are you for real!?").


After realizing that this was not an isolated event for me, I started to wonder: is this actually common for players rated, say, 2100+ Elo? Also, does anyone have any advice how to counteract this self-destructive psychological issue? Right now I'm at a loss for how to deal with it.
I am not 2000+ rated, but I experience this myself from time to time (I actually got better). 
Reasons I found why I do this:


Being to excited about my plan, e.g. I see a nice tactic, which my opponent might not see, he plays a move which does not prevent it (apart from his threat).
"I am winning feeling", I get this when I won previous games against someone and am in a winning position again. Sometimes (especially when tired) I start to "just play it down". Then I start missing things like a Zwischenzug.


For countermeassures:


I focus more on opponents threats during his time, while developing my plans during my time. If he plays an unexpected move, I take my time. This way, I am constantly up to date about my opponents threats and I distribute enough time to think about his plans. If he plays really fast, I have to spend some of my time. Since I am used to spend more time for his plans, I do this quite automatically.
If I am feeling happy about a position, I tell myself, "Nice position, lets focus and find the closing moves". This helps me to focus (again).