Your poor calculation point is according to my own conclusions. Disorganized thinking is partly right.
I give an example as feedback to your thoughts about both points in the hope of stimulating further thoughts.
This is a position with black to move of my last otb game last week. The position was new to me in a tournament game and I couldn't remember any examples about it.
First point is time control: 75 min./ + 30sec. per move for the first 40 moves. It's move #8 and the opponent had used 20 min. My clock showed 5 minutes less. Playing rarely otb-tournaments it is important to use the time in a way to avoid "Zeitnot" and on the other hand use it completely.
So was the first decision to spend up to ten minutes here. (8 min. were needed.)
Next I had in mind my intention to castle short in the background. The bishop must move. So the first candidate moves were BxN, Bh5, Bf5.
1. - BxN 2.BxB 0-0 3.d3 and I didn't like whites bishop pair and the plans with e4 or b4-b5. So BxN was rejected within a minute.
Now comes the disorganized part. 1... Bf5 somewhen Nh4 by white winning a tempo and I found neither a good home for the Bf5 on g6, e6 or d7 nor did I like whites possibility to attack with f4.
1... Bh5 didn't please me either because of white's later g4, Nh4 or Ne5 and f4 with attack against the king without seeing a plan for black.
This went five minutes. I cannot give an ordered report about my jumping from motives (f4 - Nh4 - Ne5 - Nh2 - g4) for white and short concrete move sequences. The result was a further candidate move - Nc8. In some lines the moves Qb3 and Rae1 had appeared and I thought about
Bc8 covering the Pb7 - leaving the e-file open for later Ne4 and Re8 and covering f5 in case of Nh4 against the Knight.
Bc8 was played. (Btw did this move not occur in my CA 10 database and got a bad evaluation - .68 by Rybka 3 in the first moment, but lead to a 0.0 after a prolongation of the lines at about move 15. I think the move is not that bad compared to the other moves giving a -.22 till -.29.)
Personally I register: A lack of concrete thinking and a lack of preparation when confronted with a flank opening.