You can't get blood from a stone. No, no you can't. And, what I think is much more to the point is that you are going to get incredibly frustrated and disappointed trying to do so. I think the most useful message you can get from this idiom is to remind yourself to constructively manage your expectations. Managing your expectations is one of the key principles and skills in creating satisfying and fulfilling relationships.
If you are asking something of someone, first think a bit about who they are and your history with them. Do this prior to making a request. What are their innate tendencies? What are they good at? What do they like, and what do they detest? What comes to them naturally, and what do they tend to struggle with? Look for their strong suits, and match your particular needs and requests to their particular talents and abilities. Think about what's in their wheelhouse, not just about what you need.
Heart felt intentions don't always correlate with practicalities. Just because someone wants to help, doesn't mean they have the capacity to do so. Most people are genuine in their desire and intention to help out when they can, but when they accept a request that is a personal challenge both parties often end up feeling disappointed,
I recently asked a friend of mine for some advice in a field in which he is an expert. The astounding part was his immediate and in-depth response. I hold this friend in high regard, but he isn't always the best at responding in a timely manner or following through on requests. The light bulb went blindingly bright here. This particular request sought something from him that was clearly in his skill set. It was an area where it was easy for him to help and he felt confident in performing. So, manage your expectations by managing your requests. Think about who you are asking and what are you asking for. Ask yourself it it's a fit, and set yourself up for success and fulfillment.