Literally it's 'the deal / the matter is in that'. Дело also means a deed, job, occupation.
In Polish the literal translation is Sprawa w tym, że... The colloquial translation is chodzi o to, że...
Fortunately, here it is the gramatical "то" which can never be это. So, no real choice for you :)
то + что always go together like that. Это is not used grammatically with что and который.
A brief review of grammar: when a subordinate clause works as a whole as a member of the main clause, you might have a problem sometimes. Namely, when it works as an object that is not in the Nominative.
Let's imagine you want to say "I do not believe what he told us about".
You look up "believe" in a dictionary and see that the meaning you'd like to use is expressed as верить + Dative. You also know that "what he told us about" is "о чём он нам (рас)сказал". However, "о чём" is positively NOT Dative, and the Dative"чему" will not work in "tell about something". In English "what" is perfectly fine for both clauses—apparently, in Russian it is not.
To solve this, we insert a dummy "то" as follows:
- Я не верю тому, о чём он нам рассказал.
Now, «то» does its job in the main clause and «что» works in the subordinate clause—each taking an appropriate form for the grammar you used.
(of course, you could also use верить в or you could rephrase to "I do not believe his words")
There is another situation where you need it. Very rarely do native speakers say things like "About what he told us, was very interesting". Starting a sentence like that feels very awkward. Instead, we use the dummy то and, again, get "That which he told us about was very interesting":
- То, о чём он нам рассказал, было очень интересно.
There are two uses for the verb: you can tell someone something or you can tell someone about something.
The person receiving the information will indeed be in the Dative. The information being told is in the Accusative. If you tell about something, it is о + Prepositional. It is really the property of "о".
Ah so the problem comes from combining the верить + Dative with the second part then right? Without the тому it would be "я не верю, о чём он нам рассказал" which is incorrect because the thing after верить needs to be in dative but the phrase we're using requires чём to be prepositional. If that's the case then that does indeed make perfect sense.
Lol. "As a matter of Tom!" is something I will start saying in English
What's the difference between "дело в том, что...." and "на самом деле, ...."?
"Дело в том, что" provides an explanation. "На самом деле" is "actually, in fact".
Not here. Дело в том, что is a phrase meaning "the point is" / "the thing is". Note том is not capitalized, also. том is a declension of то, meaning "that".
I feel the need to ask if права is the correct word to use here. Do Russians actually also consider "right" (side) the same as "right" (correct)??
The adjective правый (of which the права here is a feminine singular short-form adjective) means both "correct" and "right-hand". Many words are based on the root: справа (located statically on the right), направо (directional movement to the right), право (a right as in law, права is the plural form...so you have to know the context in order to get the meaning correct!).
I do not think, however, that the short forms of правый and левый are used for sides. Not nowadays, at least.