In short, architecture comes from '"black magic" of people having 'architectural visions''. Indeed, there are 3 +1 main sources of architectures:
- Intuition - architectural vision.
- Method - methodologically work through and find the best approach. It is systematic and concuous and usually document. The final architecture is derived from requirements via transformations and heuristics (e.g. tactics).
- Theft (reuse) - they've done it before it work, so I am going to use it. It is used from previous and similar systems or from literature. There is a warning however, sources may provide incomplete architecture or it may be poorly understood, tread carefully.
- Blind luck - shake the brain bush and see what falls out.
Usually, however it is a combination of these three (four). The ratio is largely dependent upon experience. At yearly stages, use methodology and theft more than intuition, later one can rely more on their ability to 'feel the inexpiable'.