In real life, you have just a moment to react and yes...one punch can kill you. It's much more common than you think. In just one county: King county, Washington (includes Seattle) has 4-6 one-punch deaths per year. In Aikido the technique is always important, but getting OFF-LINE has got to be one of the most important things you will ever learn. Getting off-line has a new significance to me after reading about this poor man. You never know how things might escalate in a moment. You never know if someone thinks they're in an old Western movie and will try to punch you through the saloon doors into the street.