One point of clarification: transition regret has been relatively rare, given the context of it being very difficult to transition (socially unacceptable, hard to find people to do the procedures, etc.). The people who transitioned had to, for the most part, be incredibly committed.

It is not a given that it will remain rare as acceptance and availability increases. It might, but it's not safe to assume, because we have no data.

Note that we have examples of other major life-altering decisions that are easier and/or more accepted, and we see all things. People rarely regret having children; people sometimes regret getting married; people frequently regret trying to commit suicide (we can't ask the dead if they made a mistake).