On mobile, YouTube cuts titles off somewhere between 40 and 55 characters depending on the device. On desktop it's around 60. Anything after that is invisible to most people scrolling past.
The algorithm also appears to weight the first words in a title more heavily for search. So burying your main promise at the end costs you twice - the viewer doesn't see it, and YouTube doesn't rate it as highly either.
The fix is straightforward. Whatever the video is actually about, that goes first. Not a clever setup. Not context. The thing.
"A History Expert Explains Why Napoleon Wasn't Short" becomes "Napoleon Wasn't Short - A History Expert Explains Why." Same words. Different order. The first version makes you work for it. The second lands immediately.
I've been applying this to client titles recently and it's one of those small changes that tends to move CTR faster than anything more complicated.
Has front-loading titles been something you've tested deliberately, or is it more intuitive at this point?