(Usually) In the places where mathematics does work really well, there are clear ways to quantify and the way we quantify can be used same for all situation, but, in the places were mathematicallymathematics (usually) fails, there is an element of non-quantitative change.
What do I mean by that? Well the thing is that, what you use measure stuff by one day can't be used another day. Say for instance, a study like economics or political science, everyday through the 'force of the human mind' there are more and more variables and generative effects occuring.
Let me give you a story to explain this, once upon a time there was a copper mine somewhere and due to environment concerns of sulfur being produced when copper is extracted, the mine was pressured to reduce/ shut down operations by a local environmental authority. Some months later, the copper mine choose a fundamentally different strategy to the problem of excessive sulfur production, they decided to turn the Sulfur into Hydrochloric acidHydrosulfuric acid. This made a lot of profit and led to the business then being focused on selling HydrochloricHydrosulfuric acid.
In this case, the initial model of the company being about copper itself is changed as time progressed. However, lets say we take a subject like physics, then the subject matter that it describes, it is so that whether we did it last year or yesterday, the experiments would show the same laws of physics are obeyed.
Essentially, the argument is that the highly effectivehigh effectiveness of quantitative sciences, at least in it's current states, relies on high levels of regularities in it's universe of discourse to work.
This is not to say math doesn't totally work in the non quantitative sciences, we can use the mathematical ideas to extract out deeper meanings of observed phenomena rigorously. For example, have a look at this presentation where Eugeina Cheng discusses how Category Theory can help one understand about Racism.