As you can see there is a dominant strategy here, which is STEAL:
Reason: If you steal, you Either get 2 pens or 0 pens, where as if you SPLIT, the only possibilities are getting 1 pen or 0 pens. So you can see that Stealing would give you a better return.
Nash equilibrium is a strategy while playing game, when a player has made a decision, and where no players have an incentive to change their strategy as no one would benefit from the change, assuming that the other player would not change their strategy.
So let say Evelyn have chosen to Steal and Kean have chosen to Split. Assuming that Evelyn would not change from stealing to split, would Kean change from split to steal? of course not! because if Kean changes, he would get nothing and he would not benefit from it, vice versa for the other column.
So, what was the outcome of this game? (SCROLL to see)
Kean: STEAL (Obtained 2 pens)
Evelyn:SPLIT (0 pens)
So, would it make a difference if we didn't collude?
Personally, I would like to admit that I made a mistake in trusting Kean! He told me that he doesn't want to lose those pens.
Yes, it would have made a difference as I would have followed the dominant strategy instead of 'trusting him'.