The entire reason why trio is proposed as useful is because of bad control flow leading to unpredictable state. That's what was discussed in the example about

The entire reason why trio is proposed as useful is because of bad control flow leading to unpredictable state. That's what was discussed in the example about file handles. The problem isn't bad concurrent control flow itself, the problem is that bad concurrent control flow enables unpredictable (or difficult to predict) changes in the apparent expected state all over your program. That's the same situation as with 'goto': spaghetti jumps are bad largely because they make it hard to think about "what is true when the flow of execution gets here here" at a given point in the program.