A disadvantage is that, in a critical position against an expert player, there may be a single branch which leads to a loss. Because this is not easily found at random, the search may not "see" it and will not take it into account. It is believed that this may have been part of the reason for AlphaGo's loss in its fourth game against Lee Sedol. In essence, the search attempts to prune sequences which are less relevant. In some cases, a play can lead to a very specific line of play which is significant, but which is overlooked when the tree is pruned, and this outcome is therefore "off the search radar".