American English is really two different languages. There's the formal, grammatically correct English that we read and write, and there's the slurred and informal English we speak.

 

In conversation, native speakers tend to relax their pronunciation so much that words sound much different than how they are written. People blend two words or sounds together and say them very fast. The result is a shortened word or phrase that's easier and quicker to say.

 

People learning English find this relaxed way of speaking very confusing. The English they read and the English they hear seem very different.