It could because they don't agree with them or they're uncomfortable dealing with them.
So critical in fact, that parenting experts report that it’s one of the most important things a parent can do to foster healthy psychological development in their children (Read: The Power of Validation by Karyn D. Invalidation is one of the most damaging forms of emotional abuse and can make the recipient feel like they’re going crazy!
Failure, or any deviation from socially defined success, is labeled as resulting from lack of motivation, lack of discipline, not trying hard enough, or the like.
Positive emotional expressions, beliefs, and action plans may be similarly invalidated by being attributed to lack of discrimination, naivete, overidealization, or immaturity.
It's a flat-out dismissal of your emotions, but emotional invalidation is especially insidious because of its subtlety.
It's a quiet erosion of your value in the relationship.