Adam Wathan, a full-stack developer and entrepreneur, emphasizes the importance of using existing software to focus on product development and marketing. He chose Gumroad for his recent product, Refactoring UI, instead of building his own payment processing system with Stripe's API. By leveraging existing platforms like Laravel Spark, Mailchimp, Fathom Analytics, Discourse, Carrd, Gumroad, Stripe, Trello, Twist, Cloudflare, and Laravel Spark, Wathan has been able to streamline his business operations and generate significant revenue. These tools help with website development, analytics, community management, landing pages, mailing lists, digital product sales, subscription billing, task tracking, internal communications, domain registration, and scaffolding for custom solutions.