I’ve heard the following statement one too many times in my career…
“We can’t proceed because we don’t have all the requirements signed off on!”
Double News Flash (my new favorite phrase): You never will.
If you ask the same people how many projects and efforts they worked on ever NEVER changed after requirements were “locked” they will probably tell you ‘none’. So why the big emphasis on having everything known when you’re just going to change a bunch of things anyway? All you end up doing is endlessly debating the edge cases and “what if’s.” When the bulk of what you’re looking to accomplish has already been agreed to.
I follow the philosophy (in work, and in many cases life) that knowing 80% is good enough for me to move forward.
Follow the 80% approach and I guarantee you, you’ll get more done. Will you have to do re-work? Sure, but you were going to do that anyway when the inevitable changes happened (as you told me they always do). As long as you agree to the most critical pieces of your project in the 80%, all you really need to do then is manage change to accommodate the rest. You’ll get started a lot faster too since it’s always easy to agree on the first 80% (it’s the 20% that takes you all the time). You can adapt as you go, you’re going to do it anyway.
So stop telling me you don’t have all the requirements. If you have 80% of them, get started and quit wasting time.