Take, for example, with this new book that's coming out: The Missing Kitten. I'm waiting for it to get back from two proofreaders (who are much, much busier than I) and I'm waiting for the cover to get done (by someone who is much, much busier than I). Unless I want to do everything myself (which would give you, the reader, and incredibly inferior cover and edited book), I must wait.
How about another example: When milking cows, they sometimes don't behave very well. The flies bite at them, so they whip their tails about to keep the flies away. Since I am in the way of the tails, I often get whipped. I could get angry and get upset. Or I can ignored it and get flyspray to keep the flies away. (Flyspray, brilliant invention.)
My point is this: don't get angry at the person, look for the root of the problem. When I flyspray the cows, it rids them of the flies, leaving me free of their whipping tails. If I help my brother with his jobs, then he will be free to work on my cover, giving me what I want. Amazing how that works, huh?
So, Patience: it's a virtue, it's important. Because sometimes you just have to wait for it.