Deciding on what's fit and what's not fit, and how to reach the right balance, is a subjective and difficult question to answer. This is why software architecture (and various other flavors of IT architecture) will always be part science and part art. This is why there will be more and more architecture specialists (e.g. security architect, performance architect) over time as complexity of software solutions (or rather system of systems) grows. And this is why architects of all flavors need to have a well rounded understanding of the operating environment - including human aspects.
In order to convince oneself that something is the right fit takes discipline, experience, knowledge, and willpower. Having the willpower to question your own decisions as well as decisions and positions of those around you is a quality of a person who is a Firebrand Architect®. Ensuring the creation of software that's fit for purpose requires pushing the limits of the ordinary. It's a quality that doesn't come easy, but it's a quality that can be developed over time.
The important adjective here is the word "right." It's the right balance of requirements, constraints, patterns, decisions, and construction approaches that enables the creation of software fit for purpose. Striving for perfect or best is not a viable approach in most situations. See next post for an example of a solution not fit for purpose.