I've watched that crash and burn.
In a building society long, long ago, and far, far away, the Movers and Shakers wanted to expand to be a full portfolio business, as big as they could be without becoming a bank (and all the regulation that would mean).
So they looked at the idea that they had a captive audience to sell to, namely all the people who had mortgages with them. All those people need insurance for their houses, cars, and holidays, they said. Probably medical insurance, broadband, electricity, home security. And there was much licking of lips in the directors' corridor.
And soon, in that land, there came a great cry, saying "How the hell do we talk to these people to sell them more stuff, yet not piss them off by sending the same flyer 6 times, incidentally that wastes money?"
Thus was born the idea of a Customer Engagement System (very popular in those days), which would theoretically connection all the accounts of a single person together, so the sales droids could see exactly which of the Society's products a particular individual had, and which were missing and therefore to be sold to the poor mug.
And they set to work, to design this beast. For beast it was. What's the meaning of an address in the mortgage system? Is it a mortgaged building (maybe not)? What is it in the insurance system? Is it an insured object (maybe not)? Why is the insured value different from the mortgage value? Are those two things the same for the same customer? Oh, and by the way, how do you know it's the same building, the same John or Jane Smith? The existing systems contained NONE of the data necessary to connect the concepts together.
The Directors threw money, hardware and software at this.Yeah verily, it availed them nothing.
That Building Society, once one of the best, is now no more than a brand name in somebody else's portfolio.