It means they are learning:
what they want;
how much they want it;
how to make a plan to get what they want;
how to stick to their plans until they get what they want.
How does all that good come from no-saying and angry tantrums?
The good long-term results come when adults are patient, calm, and understanding while remaining consistently firm about children doing what is expected of them even if they don’t want to. “I hear what you want, but you still have to get in the car.”
When they see that tantrums don’t work, they eventually learn there are better ways. For example, using their words to let adults know what they want and how they feel. When they see that being angry when they are frustrated doesn’t make the toy work or the puzzle fit together. They eventually learn that sticking with it and trying over and over again is more successful – the seeds of determination and persistence.
(See Teaching Kids to Wait – Part 2 for more about children saying “no.”)