The 123 gets primed in summer with a match or two held under the tank, while the valve is open. When you get enough to light, blow out the match and close the valve. In winter, it's usually a candle. You have to be pretty careless to heat it so much that liquid fuel spurts out of the nozzle. Under very rare circumstances in the summer, I've been able to prime it as suggested in the instructions by holding the tank in my hands. But that's more of a parlor trick, IMO, than a reliable method.
This reliable procedure is really the critical difference between the 123 and the Optimus 8R and its ilk. The latter need the pump. The optional 123 pump was often bought by unskilled 123 users who looked longingly at the 8R -- much like an appeal to Tim Allen's need for "More power!!!"
. (Me and a friend used to actually have this argument.) I was an Optimus 8R user from 1973 through about 1990. When I got back to winter backpacking I tried to find it's closest modern relative and bought a Primus Himalaya. I have had no problems in winter and the initial priming flare and subsequent jet noise give me nostalgic goose bumps every time
