Weakest chain amplification principle

What I going to say is actually obvious- but somehow I never thought that the common sense proverb saying "the chain is as weak as its weakest link" is wrong. Really, when you hear it you may visually imagine a chain with a weak link which tears when disruptive force applied to it is much weaker than force needed to disrupt the rest of chain links. So, what's wrong? The wrong thing is that this proverb usually not being applied to the physical chains. It applies to the chain of circumstances, probabilities or responsibilities. In fact the chain is much weaker than its weakest link. Really, let's say we are talking about a transportation system in some city. If there is a chance of 50% that your autobus will late and a chance of 50% that your train will late there is a chance of only 25% that you will arrive at time. So, if you're looking at set or related factors where each of them has low failure probability the overall failure probability is much higher. I call it "weakest chain amplification principle". I think this fact has interesting consequences in a lot of fields. For example in sociology: next time you hear about a 'weak chain' in politic, public sector, police, health system or whatever else you should realize that the overall situation is much worse than this 'weak chain' issue. If some politician is a bit not professional, another one does something a bit not completely legal and another one is a bit dumb all together they form a government that is not a bit weak, but really weak. Of course - all above applies only when elements or factors are strongly related, i.e. when they are actually bound into 'chain'. And this, in turn, has some interesting implication in creation of complex systems, e.g. in software development. The thing is that, taking a SW development as an example - we may note that any big software complex has its own weak chain (bugs, design mis-considerations, etc), even in its final stage. Then - why at all those big programs are able to work? Considering all said above - it should be impossible to create a stable SW product in principle. How they work then? Well, they work since usually, after some polishing - bugs became kind of sparsely spread around and not related to each other. Theyhappen in certain conditions and with relatively low probability. And then the weakest chain amplification principle doesn't apply to them. p.s. Small note there is an obvious connection between above considerations and 'explicit boundaries' and 'autonomous evolution' principles in SOA.