The filter we are talking about is the mind. The mind is only interested in itself, it's not your friend, it doesn't care if the information about reality is going to reach you: it is only interested in itself right. So only what fits in with what's already in the mind is going to be relevant for the mind. Inside this context there are two kinds of filters
Filter 1: filters out information. creates a giant jigsaw puzzle, and fills in the missing information from its own database. Imagine getting two pieces of a 100-piece puzzle. You don't have the box cover with the image of the finished picture, but the mind is going to oblige and make it up for you.
Your life feels repetitive and boring, always the same, mostly misery. Why? because the mind uses the same box-cover picture for all information that comes at you: the same boring, repetitive, always the same, mostly misery picture.
Filter 2: the mind distorts the incoming information. For the mind Everything is the same as everything else ... except not always.
For example, for person A everything is a proof that they are not loved. No matter what you tell them, that's all they hear. You tell them you love them, and they know that you have an agenda, because you really don't love them.
Person B knows that they are stupid. Every time they do something right, every time they have a success, proves more and more that they are stupid. Makes sense? It makes sense for the mind.
The onlooker is puzzled, but once you understand that the filter distorts, you understand.