In Bereishit 3:22 Rashi says the following:
and now, lest he stretch forth his hand, etc.: And if he were to live forever, he would be likely to mislead people to follow him and to say that he too is a deity (Gen. Rabbah 9:5). There are also Aggadic midrashim, but they cannot be reconciled with the simple meaning.
In Bereishit 4:8 we see something similar:
And Cain spoke: He entered with him into words of quarrel and contention, to find a pretext to kill him. There are Aggadic interpretations on this matter, but this is the plain meaning of the verse.
In both cases Rashi is hinting to us that there is more to explore but is not actually giving us all the details. What exactly is Rashi trying to say with these two verses?