With mathematics, everything is logical; there is no "guessing" and no "maybe", only logical
reasoning.
We associate the minus sign with opposite (as in give and take).
For example,
-8 means taking away 8, while (+)6 means giving 6
So -8 + 6 translates to
taking away 8 and giving back 6
which is equivalent to taking away only 2
But taking away 2 is what is meant by -2 . That is why -8 + 6 = -2.