my lifetime retention is only 22% (average view duration 2:14) so don't worry, it will increase the more you build loyal viewers. It's most likely people stumbled on the video somehow and didn't want to see the rest. It's because people don't want to watch long videos from an uknown YouTuber as they feel it might not be entertaining enough. Unless they're familiar with your personality or something, then they most likely will watch it all. Wade/LordMinion777 is a good example. He leaves the boring-ish stuff in a lot of the time and even has videos hitting up to 40-50min long but people still watch till the end because that's Wade, not all the time something interesting happens but you know when somethin happens in his video it's worth watching the whole video to see lol That's pretty much how it is for a lot of gaming videos too. It's why I spent nearly an entire week working on highlight videos for my AC4 playthrough, since I've finished the playthrough, now I can do them to give people a taste of what happens in the playthrough and as a thank you to the people who watched from start to finish.
My tip which is actually kind of a common sense 1 is to make highlight videos whenever you have the time, nice and short <4 mins. Because let's face it, games aren't just little 5 min things you can just whip up, people will say to keep your LPs short at 5mins but then it's not a LP lol. I'm keeping my AC4 highlights at around the 3min mark. Look at SeaNanners, his videos don't go longer than 3 mins and they are nothing but the best parts from his play sessions, he also does it in a way that it drives people to the channels of those he plays with as they put up the longer versions. He didn't always used to that though, he used to do longer LP type videos on CoD a long time ago. Markiplier likes to make highlights of his entire channel now, as in every video he can grab stuff from. Two Best Friends Play make highlight videos lasting up to 1hr long lol