If you set up a date with someone and they cancel last minute with "can we raincheck?" and didn't come up with a legitimate reason why they need to cancel, 9 times out of 10 this probably means they either found another date that they chose over you, or they just simply aren't interested enough to follow through. Probably best to assume the date isn't going to happen.

Learn to recognize the signs that someone isn't interested and move on. You should only be interested in those who are interested in you.

Don't waste time with those who don't value your time.

UPDATE: Alot of the awesome comments below have reality-checked me and made me realize that I am taking a very pessimistic view of the situation described above. Just wanted to say that I greatly appreciate the honest and un-restrained feedback this community has given me day after day. Thanks again everyone!