The adverbial “although” means the same thing as “despite the fact that”. We use “although” at the beginning of a clause which contains information that contrasts in an unexpected or surprising way with information in another clause. For example:
Although it was raining, we went for a walk.
If it is raining, it is surprising that we went for a walk. The walk happened despite the rain. You can also feel that first it was raining, then we went for the walk. We cannot say this:
Although we went for a walk, it was raining.
If we went for a walk, it wasn’t surprising that it was raining. We probably already knew it was raining. The rain did not happen because of the walk. The rain was not an unexpected result of the walk.
Now let’s try but:
It was raining, but we went for a walk.
The coordinating conjunction “but” emphasises the joining of two contrasting ideas. In the above sentence, you can feel that the two ideas contrast with each other. As a result, you can flip the sentence around.
We went for a walk, but it was raining.
You can add “but” to either of the clauses, but you can’t add “although” to either of the clauses. The coordinating conjunction “but” joins together two equally contrasting ideas. The adverbial “although” does not join together two equal ideas – one of the ideas is an unexpected result of the other clause.