20 years of software development taught me three very important lessons; 1️⃣ Unit and integration tests are the best way to prevent bugs. 2️⃣ Keep it simple! In the long run, simple solutions can better adapt to new requirements. 3️⃣ Debugging through OSS code (Spring, Hibernate) will teach you how to use the tool properly and will provide you with real-life examples of when to use certain Design Patterns.