Why was this Twin-Otter Take-Off unsuccessful?
Comments under the video say clearly:

According to Transportation Safety Board (Canada) report # AO7W0128,


Take-off weight did not meet performance capabilities of the Aircraft.
Calculations to clear 50ft obstacle were not performed.
Southeast end of runway, not clearly marked.
Take-off was attempted in an up slope direction with a slight tailwind which increased the necessary distance to clear a 50ft obstacle.
Center of gravity (CG) calculations were off and found to be too far forward.