Typically, establishing milestones and the credibility you can accomplish them is what enables an investment. People want to know what you are going to accomplish with their money. I find it's usefule to report your progress toward milestones and as well as any new information that would be useful in suggesting that new milestones may be more important than those on the current plan (pivots, new strategy pending, etc). I always assume you want your current investors to be future investors and that you should treat them the way you would wish to be treated in their shoes. On one hand its' seriously not OK to offer milesstones you have no intention of working to hit. On the otherhand, it's not OK to continue to work toward milestones you have learned will lead nowhere. Be forthcoming in what you want to achieve and put investors on notice that learning may change the milestones.