I think there is just something about the basic psychology of people that makes us very sensitive to the perception of delaying other people- I think it is tied up with idea of self-esteem- if we hold up other people then many people feel uncomfortable and stressed because they have low self esteem and don´t feel that they are worthy of holding other people up- this applies even if they are not the direct cause of the delay such as a car driver following a cyclist because they feel they have a duty to get past you and not hold up other drivers behind them. This type of driver will try and pass when it is unsafe but (unintentionally) sometimes hit the cyclist. In this case I feel it may be a relief to many drivers if it is clear that there is no way they can get past you as then they cannot be responsible even in part for the delay. This is why taking the lane can be a good idea in some circumstances as it takes away the responsibility for the delay from the driver behind you.

On the other hand, there is (fortunately more rarely) the narcissistic driver (I´m Ok you´re not Ok) who feels that you should not hold them up because by doing this you are basically saying "I am more important than you". This is perceived as an attack to a fragile ego and an attempt at belittlement. This triggers a defensive attack.

The problem for the cyclist is that you dont know at the outset with which type of motorist you are dealing.