The most important rule is understanding the context of any design guideline, rule-of-thumb, "pattern" or "best practice". Something like the Open/Closed-princ

The most important rule is understanding the context of any design guideline, rule-of-thumb, "pattern" or "best practice". Something like the Open/Closed-principle is a really great principle for the kinds of projects if was created for. It is just that for 90% of software development it is not appropriate and therefore leads to needless complexity. Discussing whether SOLID is good or bad in itself does not make any sense IMHO.