Love.
In its purest form, it is unconditional and yet we were taught as children that it is given upon certain conditions. If we behave "this way", we are rewarded with love and if we do not, the punishment is the absence of that love. Now, our parents meant well by this, teaching us right from wrong, and discipline is necessary to ensuring a strong sense of morality. However, well intentioned or not, it developed into a mindset of trying our entire lives to "earn" love through give and take.
This mindset doesn't allow for us to fully embrace all of what Love has to offer us, because the fear of losing love before we have even attained it, is present.
Letting go of that mindset and fear enables us to be enveloped in the full vulnerability of Love without condition. As it is intended to be. The same way you'd love a field of flowers for instance. You wouldn't go up to each flower and critique it to determine whether or not it was worthy of your love. Nor would you need the love you've given to be reciprocated by the flower in order to give it. You'd simply give, without condition, your love to it for being just as it is. A beautiful part of the collective existence.
So, if we can love flowers in that way, then I'm sure we can love one another in that manner as well.