"Oh Shit" moments...

Had my first oh shit moment on saturday. Was in herne hill not sure of the road name and I was cruising along, had a van pull out and try and do a u turn basically covering the whole road. I've been riding without a lockring since 400AD and just a bit of loctite but i had to pull up sharpish here and I got the rear wheel locked up and then bang no tension i couldn't do anything pedal forwards or backwards. Thought i'd dropped the chain and was bricking it thinking the rear was gonna lock up but it didnt, ended up scraping my shoes along the ground mounting the pavement and sticking my foot in a muddy verge to stop almost ripping my leg off. Next day I got a lockring lesson learnt the hard way

Why not have a brake as well? This is the reason why two braking mechanisms are a legal requirement.