Clarify "The problem has to exist" in the best practices

Simply saying that "The problem has to exist" from the start may convey
a wrong subconscious message that problems must exist in the engine for
the sake of it, especially if taken out of context, so it's better to
make this more explicit to mean that "problems can only be solved when
they actually exist" up front.

community/contributing/best_practices_for_engine_contributors.rst

@@ -46,20 +46,19 @@ as source and binary and requires maintenance once it exists. Avoiding the
 addition of anything unnecessary is always considered a good practice in
 software development.
 
-#2: The problem has to exist
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+#2: To solve the problem, it has to exist in the first place
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-This is a variation of the previous practice. I believe most developers agree
-that adding anything unnecessary is not a good idea, but what constitutes what
-is necessary and what isn't?
+This is a variation of the previous practice. Adding anything unnecessary is not
+a good idea, but what constitutes what is necessary and what isn't?
 
 .. image:: img/best_practices2.png
 
-The answer to this question is that the problem needs to *exist*. It must not be
-speculation or a belief. The user must be using the software as intended to
-create something they *need*. In this process, the user may stumble into a
-problem that requires a solution in order to continue, or in order to achieve
-greater productivity. In this case, *a solution is needed*.
+The answer to this question is that the problem needs to *exist* before it can
+be actually solved. It must not be speculation or a belief. The user must be
+using the software as intended to create something they *need*. In this process,
+the user may stumble into a problem that requires a solution to proceed, or in
+order to achieve greater productivity. In this case, *a solution is needed*.
 
 Believing that problems may arise in the future and that the software needs to
 be ready to solve them by the time they appear is called *"Future proofing"* and
@@ -69,9 +68,9 @@ its characterized by lines of thought such as:
 - I think users will eventually need to...
 
 This is generally considered a bad habit, because trying to solve problems that
-*don't actually exist* in the present will very often lead to code that will be
-written but never used, or to code that is considerably more complex to use and
-maintain than it needs to be.
+*don't actually exist* in the present will very often lead to the code that will
+be written but never used, or the code that is considerably more complex to use
+and maintain than it needs to be.
 
 #3: The problem has to be complex or frequent
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~