Transitions Confusion

I was having difficulty inserting any sort of transition between my clips - this happened to be video of a band. I researched the issue both here and on the internet and understand the issue to be not enough info at the end and beginning of the clips for Resolve to process a transition. I'm told the solution is to trim a couple of seconds of clip from the end of one and the beginning of the other and then transitions work.

Sure enough, this worked. But I don't quite understand what trimming the clips accomplishes. Once you trim is the info still there? How can that be if that portion was trimmed? And if the info is still there, it was also there before the trim, so why the need to trim?

I know I am fundamentally missing something so I hope to have this clarified. The transitions not working also occurred in Premiere Pro, so I know it is a user issue. "what" needs to be done but not "why".

Thanks all-

The why is because the transition is performed on the 'handles' of the clip which you create by trimming.
I'm not 100% sure but I think the newer fusion transitions don't need these handles to operate on, I haven't had chance to test this yet though, no doubt someone else who is less of a hobbyist knows

Thanks Dave. That sort of makes sense - but if you can manually set say a 2 second clip on each end, it sure would be nice if there were a way to automate this; i.e. automatically trim 2 seconds on each end every time a transition is inserted. There must be a way to do this I'm hoping.

The why is because the transition is performed on the 'handles' of the clip which you create by trimming.
I'm not 100% sure but I think the newer fusion transitions don't need these handles to operate on, I haven't had chance to test this yet though, no doubt someone else who is less of a hobbyist knows

I just tested it now with two "not trimmed clips", the new transitions are acting like the other ones, you can't apply them, they need to be trimmed.