Having worked with several startups at different stages of their life cycle and despite them targeting completely different markets, developing different products, having different teams, using different tech stacks, and so on - I found that almost always they are following the same way and keep repeating same mistakes in solution and system design and areas corresponding to it, such as defining MVP, defining product features and approach to development.

No matter how small your startup is and how agile your processes are, you are still making architectural decisions and that means - effectively practicing software and solutions architecture, consciously or unconsciously.