Irrational desires offer no security: they can easily be gone the next day. Rational desires do: the fact that I can articulate the reason for their existence - trace them back to their root - means they are more likely to stick around.
Flipside: Justifying a goal hardens it. Even when my heart is not in it anymore, I still work towards the goal inertially, by telling myself the reasons why it was important to me.
cf. Minsky in Society of Mind: how can we set goals for ourselves years into the future?
This made me think about love: how can people put so much faith in their own feelings, to follow them and not think about whether that feeling will stay years into the future?