Why don't people actually do what they say the will??

I was thinking about this a work the other day, since it's usually just me sitting there for 7hrs with nothing to do but think. Anyway, I was thinking of all the different times people had told me things and then never actually acted the way the said the would or did the things that they said they would. Why is that? We're they just lying to me to avoid hurting my feelings or making things harder on them or did they truly intend on acting or doing they way the said but just hadent got around to it. I have a feeling it was the first one which sucks because being me I belived that they would actually act and do what they said they were going to do which gives me a stupid sense of false hope. However, maybe I am wrong maybe they do have good intentions. who knows.