Theory vs reality: How to build a personalisation platform for 30M users and not go bust in the process

Personalization promises to boost profits across many industries, but in reality, difficulties and costs may often outweigh the benefits. How to choose an appropriate algorithm and modelling approach, when reality doesn't fit theoretical models? How to ensure cost-efficiency & future-proofness not covered by academic research? How to respond to changing business requirements in no time? 
Go beyond research papers - draw from our experience of building a pragmatic, real-world personalization platform for 30M users of a major European media group.