This is a fairly common request from companies that are just beginning their journey to implement EOS. When this question shows up, I offer two rules to help them stay on track:
Rule 1 - Always do the right thing for the business.
If that means something else is really more important than the Rock, or you see the Rock should simply not be done (maybe your world changed somehow) - DO THE RIGHT THING FOR THE BUSINESS.
Rule 2 - Don't change the Rock after it is set.
If it does not get done, it is a MISS. Take the MISS as feedback on your process - and on your current ability to PREDICT. Ask yourself... How could we have known that something else would become more important? How could we have known that something else would actually need to happen first? You get the idea. Think about how you can improve your ability to predict.
As for that current Rock in question, you have a choice:
1) do nothing about the Rock & divert your focus to the new priority instead. Come back to the Rock after the new priority has been addressed. Accept that you may MISS the original Rock - depending on how quickly you get back to it.
2) work on the Rock in parallel with this new priority - giving yourself an opportunity to still HIT the Rock. Remember, you really did think the Rock was THAT important when you set it.
Simply decide what's right for the business - and lead with the example you want to set for your team. Easy, right? ;)
Take heart. Everyone on the leadership team will learn a lot during the initial rounds of Rock-setting - and everyone will do even better on the next cycle through the process. And that's a big part of what we call TRACTION.
Stay focused on your Rocks!