If a video is 30 seconds or under, it's very likely that most people will watch it all the way through.
If the message is more complex, then take time to explain it, but understand that half of the audience won't make it to the end of the video. With this in mind, a video should be front-loaded with the most important parts of the message and be compelling enough so they might view to the end.
Understanding the relationship between video length and viewer engagement can help you ensure that your audience is getting the most out of your videos.
Now let's briefly get on that surfboard...