What is problem behaviour?

In short: exhibiting behaviour that is unacceptable to us. I say with emphasis: unacceptable to us. Because from the cat's point of view, it is certainly not always about problem behaviour.
In many cases, it is the case that the cat is somehow unable to exhibit the behaviour it would exhibit under normal (ideal) circumstances. In its way, the cat will start trying to make it clear to you that not everything is the way it likes/experiences it. Making this clear can be perceived by people as problem behaviour, and in practice it usually is. After all, it's not really nice if your cat is, for example, house-trained, aggressive, scared, or scratching the walls. However, there is a nuance to be made between one type of problem behaviour and another.
Scratching, for example, is natural behaviour for a cat. However, if the cat scratches the sofa or the wallpaper (for whatever reason), then we as humans have a problem with that.  Unwetting, on the other hand, is not a natural behaviour for a cat. A cat will be housebroken from kitten age. If it is not, this is a sign that something is wrong. This may have a physical cause. For this reason, when a cat has a potty-training problem, a veterinary examination will always be needed first.
But natural behaviour or not: any behaviour you have a problem with as a cat owner is problem behaviour. And that's where I can help you.

Scratching is natural behaviour for a cat, but unwanted on the sofa or wallpaper.

I am not a cat whisperer, I do not possess any special gifts to communicate with cats in a different way than other people. What I am is a person who has gained knowledge about cat behaviour, body language, etc. through serious training.
After all, cats also communicate, just like humans and other mammals. The problem, however, is that we as humans, look at cats' behaviour with our human eyes and more importantly: start interpreting it in a human way. This is where things often go wrong. Not because the good will is not there, but because cat communication is substantially different from ours.
In this way, a cat may display certain behaviour where it often wants to tell us that there is something that displeases it, or makes it unhappy. Behaviour that is usually in bad taste with us humans. So problem behaviour does not come out of the blue, nor is it a cat's way of "teasing you" It is a serious request for help and comes from somewhere. From where? That is what I, together with you, will look for. This is called the motivation for the behaviour by a cat behaviourist. And only by asking a lot of questions can I find out where your cat's motivation for a particular problem behaviour lies. So I am not going to fight the problem alone: this is patchwork. But I will dig thoroughly for the real motivation and address it. Among other things, I work according to the learning principles as developed by various behavioural psychologists.Of course, I can do this