Why are SOLID principles important in software development?

SOLID principles are important because they address the fundamental challenges of growing software: rigidity (hard to change), fragility (breaks in unexpected places), and immobility (hard to reuse components). Following SOLID leads to code that is easier to test (isolated responsibilities can be unit-tested), easier to maintain (changes are localized), easier to extend (new features don't break existing code), and easier to understand (each class has a clear purpose). While they require upfront design effort, they pay dividends in long-lived projects where requirements evolve. They are especially critical in team environments where multiple developers work on the same codebase.