[quote=ShadowVentus]
We all summon our keyblades and fire beams of light at the tendril, having it shrink away from the light.
[/quote]

The tendril of Darkness is hit b the light, and it curles around it. It absorbs the light, and the light becomes nonexistant, as it fades away, the Darkness spreading towards you. However, the light made it hesitate. The combined power of three keyblades made it hesitate, and thus, it can be stopped. It could possibly have weakness, it can be fought like a normal enemy, albeit a powerful one. It's not the unstoppable, infinite source of pain and death that your minds' fear had conjured up, the image spawned from your sense of impunity before it. This alone, gives you hope to face it, as the shroud that kept you from doing anything much is lifted, and finally you're able to move freely and with speed.