Taiwan recently held a public testing of missiles. Officials were surprised, and embarrassed, when 32 percent of the missiles (surface-to-air and air-to-air) failed. No one should have been surprised at such a failure rate, as it is not uncommon. Last year, the South Korean Navy was embarrassed by revelations that 20 percent of its SM-2, Harpoon and Sea Skua missiles test fired over the last few years had failed to hit their target. Some of the failures were due to operator error, but more of the problems were because of defective spare parts and maintenance issues in general. The Taiwanese will probably find that they are suffering from the same problems. Any nation that uses these complex missiles will find that they are at risk of failure and humiliation.
Modern missiles are usually stored in a sealed container, which they are often also fired from. Sensors monitor the state of missile components, and these are replaced as needed. Missiles that don't use these transport/firing containers, often have a similar container for storage, and, increasingly, monitoring of the missile. But after a while, it's time for a refurb, or dismantling and disposal. Generally, this system works well. For example, over the last quarter century, the U.S. Navy has bought over 6,000 Tomahawk cruise missiles, but fired only about 2,000 of them in combat or training. As the older missiles age, they must either be destroyed , or, along with their storage container, refurbished. Lately, the U.S. Navy has been refurbishing about 250 Tomahawks a year, at a cost of about $200,000 each. It's a lot cheaper than buying new ones.
More recent models of the Tomahawk are equipped with sensors that report the status of many components, enabling missiles to be kept in shape with periodic maintenance and replacement of failing components. This does not eliminate refurbishment, but makes the process less frequent and cheaper. This approach typically achieves over 90 percent reliability for the missiles fired. But it requires 24/7 monitoring, and prompt replacement of defective parts.
While South Korean and Taiwanese officials were upset at the lower reliability rate of their own missiles, they were also quietly informed that you have to spend more money on missile maintenance to get 90 percent reliability. Moreover, some pundits in Taiwan believe that the government allowed the media to witness these tests (for the first time in two decades) because of the belief that the results to help convince the United States that more high-tech weapons should be sold to Taiwan, and that Taiwanese politicians should come up with more money for missile maintenance.