Aurus Huang has explained the words very nicely, I would like here, to supplement on this phenomenon generally.
Like this character 呆，it is pronounced dāi if you look it up in dictionary. However, its correct pronunciation was once ái. A disease named 呆小症 was supposed to be pronounced as áixiǎozhèng. But for whatever reason, people did not like the way ái is sounded and persisted pronouncing 呆 as dāi. The dictionary finally surrender and denote 呆 as dāi.
This is, though not common, but rather normal in a language, not only in Chinese. When a majority of people is pronouncing some word or character in a way that is different from the literature, this "wrong" pronunciation may eventually become "correct"!
There are other examples in Chinese like
确凿，quèzuò to quèzáo
唯唯诺诺，wěiwinuònuò to wéiwéinuònuò
There are more examples here.
Such changes can happen in English as well.
I was wondering why "k" does not pronounce in words like knee and knock. But in fact, in ancient English, they do hold a position in these words' pronunciation! However, English spelling is fixed way before its pronunciation did. Letter "k" ceased to pronounce soon after the spelling was fixed but those words are still written in its original form. Not to mention, pronunciation is still changing nowadays!
Many other words have changed their pronunciation along the way and it is quite an interesting story.
By the way, the word coyote is having so many different pronunciations that it is making people so confused and asking questions like this!
In conclusion, when speaking, just pronounce the way you feel natural and comfortable with, but in case of an exam, go with the textbook!
Language is always first a communication tool and then a cultural symbol, so it should fit people who have been using it rather the other way around.