Eraser dosent erase just lightens the color

I have been trying to use my eraser and when I click on something it only lightens the color not erase it. am I being dumb or did i do something

Have you checked Opacity tool parameter at top panel where there are also Eraser shape and size and Pixel Perfect checkbox? It should be 255 for Eraser to fully erase content. Else it will make it translucent.