Star Trek: 10 Crazy Facts About The Trill
4. Combined Personalities
The process of joining was obviously highly beneficial to the symbionts considering they need the Trills to survive. But the Trills also got something out of the process, too.
Joining with a symbiont meant that all of the memories, experiences and knowledge from the previous hosts were now passed down to the new host. In the case of Jadzia Dax, there were seven previous hosts that were now rattling around in her head. That included Curzon Dax, who had a pretty big personality.
While having access to all of these resources can be incredible, it also came at a price. The impact of having all of these new memories rattling around one's mind from the symbiont is that it changes the personality of the host. Friends and family from their pre-joined days have often reported that the host seems a lot different.
Jadzia started doing a lot of Klingon stuff and playing Tongo with the Ferengi. These were things that Curzon loved to do, and Jadzia never did before joining. A huge part of the training prospective hosts are put through was learning how to deal with all of the new memories and personalities. There's a reason why joining isn't right for every Trill.