>> Managers like numbers, estimates, and asking for estimates with an idea written on a napkin. It's just how the real world works — a business has some monetary goal, but before committing to it, it needs to understand how much it will cost. I think everyone squirms when asked to make a prediction with too little information. If you want to see a developer squirm. ask for an estimate for how long it will take to bui…
Product/feature value usually spans a larger range of values than time to build it, so you don't need to estimate value as accurately for it to be a useful guide. It's also often easier to estimate because you wouldn't consider building it unless you have potential customers lined up.
And then if the PO says "building this feature would earn us back 2 developer-months in the first year alone" it's usually very easy for a developer to judge if building it fits into that profit window or not.
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Of course, nobody does this in practise because people suck at decision-making. The next time someone asks you "how much will it cost?" try asking them "how much is it worth our organisation? What are we willing to pay?" and it will be clear they have done zero analysis on cost/benefit.
People don't know how to analyse -- or are uncomfortable with analysing -- these things so they are looking to be guided by their emotional response to information.