An invitation; an obligation?

So, I have come upon an intersting social question. Is an invitation, an obligation? If someone invites you to do something, do they oblige you to do it? Now, the case that raises the question is not really an issue, the subject is still aroused. The case was that Jaize invited my to Six Flags Elitch Gardens next week. Now, I am totally looking forward to it. Honestly, I could think of no better way to celebrate me getting out of school. As this adventure takes place the day after my last day in ALL of my classes. WELl, actually, my Calculus and Physics classes end the day before (May 2nd) and my Chemistry class ends the day right before (May 3rd). SO, since this takes place May 4th, I am happy to attend, even outright blissful. But, in another invitation, I felt as if the invitation was more of an obligation. I am not sure. Have you ever felt that? When an invitation felt more like an obligation? I am really looking forward to this weekend, and next week. AAAHHHhhhh....

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"The end is so near, the excitement has already passed." -- Rossi Guiliani