Acknowledging: The most basic level of self-validation is simply acknowledging the presence of the emotion rather than judging it; for example, telling yourself, I feel unhappy. Just acknowledging or naming the emotion and putting a period on the end of the sentence rather than going down the road of judging it validates the emotion.
Allowing: The second level of self-validation is allowing, which is essentially giving yourself permission to feel the feeling; for example, telling yourself, It’s okay that I feel unhappy. This takes not judging the feeling one step further, affirming that it’s okay to feel this way. This doesn’t mean liking the feeling or wanting it to hang around; it just means acknowledging that you’re allowed to feel the emotion.
Understanding: The highest (and hardest) level of self-validation is understanding. This level, which goes beyond not judging the emotion and saying it’s okay to feel it, involves having an understanding of it; for example, It makes sense that I feel unhappy, given the difficulties I have managing my emotions and the chaos this causes in my relationships and my life.
Source: DBT Made Simple