I think too much has been made of the players 'downing tools'. Look at the derby and the Leicester game for example, and you'll see that many of the problems stemmed from lack of organisation and a lack of belief. In both games, the players were trying to cling on but then lost all belief once the game got away from them. They then became a shambles. No player would ever down tools in a cup semi final, particularly our players, many of whom don't have/may never get a winners medal - but they still lost that game in 90 minutes, and were thoroughly outplayed for half the game.
A few people have used the example of everyday workers, and it does ring true. It's very easy for things to spiral once things start going badly. A couple of years ago I went through a period when I just couldn't hit my monthly targets, and the longer it went on, the worse my performance got. It's a vicious circle, where your confidence drains away and your willingness to take responsibility and put yourself in the firing line diminishes. It's not a case of downing tools, simply that an irreparable breakdown of trust and belief has a massive effect on performance.