Conversation abbreviated to pertinent part...
"Pardon me sir, can you help me find the stop for XYZ Bus?"
"It may be a bit far to walk..."
"That's OK, I don't mind walking a bit. If you know precisely where it is, please tell me."
"Well, you walk about thirty blocks that way..."
"Obviously, you don't know where the XYZ Bus stop at this depot is. I'm sorry to have disturbed you, sir. Have a great day." (Walk away.)
Yelling after me: "Then why did you ask me in the first place?"
Because unfortunately I can neither read minds, nor predict the future, nor even detect someone who actually has the information I'm looking for. At this point, I'll settle for someone who, if they don't know the answer, will at least be up front about it.
Takeaway: Not knowing the answer to a random stranger's question is OK. Wasting their time when you don't know the answer isn't. (Not to mention they'll find out anyway!)