Yes, one lives and learns...
White smoke out the exhaust means you should immediately shut down the engine.
Head gaskets do fail now and then, with a great degree of unpredictability. A friend bought a Dodge truck and a head gasket blew while he was following me on the highway. HUGE cloud of white 'smoke' (likely steam), and I-75 in Central FL was almost a white-out for about 5 minutes. He tried to start it for me, and it wouldn't crank. I knew then that the cylinder(s) was/were full of coolant. A tow job and new head gaskets fixed the problem with no other engine damage. The trick is to catch it in time.