Software should be robust. It should be designed to accommodate all known edge cases. In practice, this means predicting and handling all known error cases, enumerating and addressing all classes of user inputs, reasoning about and planning for the performance characteristics of your program, and so on.
Software should be reliable. It should be expected to work for an extended length of time under design conditions without failures. Ideally, it should work outside of design conditions up to some threshold.
Software should also be stable. It should not change in incompatible or unexpected ways; if it works today it should also work tomorrow. If it has to change, a plan shall be written. Stakeholders (including users!) should be given advance notice and should be involved in the planning stage.
Finally, software should be simple. Only as many moving parts should be included as necessary to meet the other three goals. All software has bugs, but complicated software (1) has more bugs and (2) is more difficult to diagnose and fix. Note that designing a simple solution is usually more difficult than designing a complex solution.
This (short) article is based on a Mastodon post I wrote a few weeks ago.