An obligation is something you may not like or even enjoy doing but you do it out of respect or some profound sense of duty.
Don't ever tell your girlfriend that you're attending her 21st birthday party out of obligation. She's not American born and English is her 2nd language; she doesn't fully understand its definition. She has absolutely zero respect and will never have any sense of duty. She will fight with you for days over the true definition of the word, implying that somehow, duty has a "negative" connotation. As she verbally castrates you, you will be constantly reminded of how pussy-whipped you are and how she abuses your fear of being alone to her advantage. Your relationship with the man eating bitch, no matter how gorgeous she is, will strongly parallel repeatedly running head first into a brick wall and loving it. Even after you’ve accepted defeat, admitted your wrong doings, and apologized for them, she will continue to berate you over the fact that she is never wrong.
Four years of college… wasted out of fucking obligation.
Dick: "Actually, urbandictionary has a pretty good definition you omnipotent whore."