[normaljoe]

As the other posts point out it's not just a matter of material, but a trade off. As you increase the ductile strength you end up with something that is more brittle and the same is true in reverse.

Brittle materials are more temperature sensitive and can rapidly fail. Brittle fracture is no joke look for WWII Liberty ships split in two as an example. We didn't really understand why at that point in time.

The answer though is actually pretty simple and why you can't get a perfect material. The lattice structure of the molecules connected to each other can be soft (plastic) or hard (steel).

In the plastic example just take a milk jug and poor boiling water into it. Don't actually do this without protective gear (oven mit should be fine). The molecules holding everything together get excited from the energy (heat) move around and since they are not closely bonded end up in a different configuration. Your milk jug at this point does not look the same and is deformed.

In the hard example just boil the water you are using for the plastic test. The pot you used does not change because the molecules are tightly bonded.

It turns out the the tighter the molecules are bonded there is still a point where that bond will break. Hence the brittle fracture, which is every molecule mic dropping and going home at the same time.

While I could go down another rabbit hole to the atomic, subatomic, level of how those lattice structures work. I won't as I think this example gives you what you need.

Finally in this case we have a very old, by modern space technology, structure that is made of material that was most likely never expected to last this long. If you want a space ship to last you just have to make sure the engineers understand what "last" means. :)