Spend some, obviously. But when you have worked out a stunningly precise plan for a project you know that three things will happen, starting with:
1) Some of it will work out exactly as you intended and it’s great
Happy for you. But then:
2) Some of it will be wrong
You will have made mistakes, you will have misunderstood something. And:
3) Something unexpected happens
There is always something unexpected or it would be in your plan and you’d call it expected.
What worries me and occupies me a lot about this is how fragile we really are. You hear about impregnable secure places that get broken into because the plan didn’t consider that baddies could be hiding in the laundry truck. The greatest, biggest, best-defended castle is taken over because who’d be suspicious of those two monks?
There is a saying that you should hope for the best yet plan for the worst. Fine. But don’t plan too much because it’s pointless.