Question: how/why does blood clot?

Rebecca Roddan answered on 4 Nov 2018:

If blood didn’t clot, you wouldn’t be able to stop bleeding and lose lots of blood. This would be really bad for you and could eventually kill you. This is the case with people with haemophilia (famously members of the Russian royal family in the 1900s suffered from this and the illness is genetic so is passed through families) and means that they have to take different drugs to help their blood clot. People suffering from haemophilia have to be really careful about getting any kind of small cut as it would be really dangerous for them.

It clots because different cells and proteins in your blood work together to stop it.