Doubles are among the easiest addition facts to learn.
This is possibly due to symmetry or repetition of the addends. Deriving from doubles means using a given doubles fact to find new results.
For example, knowing 5 + 5 = 10 can be used to solve 5 + 4 = 9 by partitioning one 5 into 4 + 1.
Addition and subtraction as inverse operations can be used to solve 10 – 5 = 5.
This is further explored in the big idea of fluency and flexibility.