I find the list of little help. Yes, these points might be 'deadly sins', but just pointing me to RabbitMQ or advise 'feature flags' is of little help. And why

I find the list of little help. Yes, these points might be 'deadly sins', but just pointing me to RabbitMQ or advise 'feature flags' is of little help. And why is 'optimizing and tweaking' queries necessary for scalability?