An egg can be hard-boiled, but it can also be soft and runny - easy to poke, easy to squash, providing no resistance. In other words, it can be extremely delicate - just like a person who is scared of everything. So it's not surprising that the word "Weichei" - literally "soft egg" - is what the Germans use to describe a person who's the opposite of tough. It's the sissy, the wuss, the wimp, the softie… But just don't call them too many nasty names or they might get angry and throw something at you - maybe an egg.