Who would have thought such a simple word could cause so many problems? Chinese pronunciation has a few “tone change rules” which linguists call “tone sandhi”. The infamous 3rd tone has one of these rules, and many westerners who study Chinese never learn it in their beginner days of study.
The “Tone Sandhi” rule for 3rd tone:
If you have a word or phrase that has two third tones consecutively, the first of the two changes to a 2nd tone. The most obvious example of this 你好 nǐ hǎo. Many foreigners surprisingly pronounce this most simple of words incorrectly, because according to this rule, the first pronunciation nǐ needs to transform to ní (2nd tone). Most of you probably use “Pleco” as your dictionary app, and even Pleco does not show this tone change rule, you have to remember it yourself. But just like all of Chinese, you’ll get used to it :).
Its always important to remember with rules like this that the point is not to take loads of time thinking about the rule and agonizing over whether or not you are following it (a similar principle applied to learning grammar rules). The point is simply to allow yourself to notice it when you hear Chinese speakers and when you learn a new double 3rd tone word. By being aware of the rule, you automatically increase your likelihood that the next time someone says it you will have the ability to recognize it. That recognition ability is what you are going for, not the ability to recite the rule. After a long enough period of recognizing it, it stops being a conscious process, you just automatically imitate, its great. 加油！