Given the J's need for scheduals, planning, and organization, and their general uncomfortablity with the spontaneous, one would expect them to dislike surprises. This is probably true, for the most part. Yet surprisingly, my mother, who is an SJ, likes things like surprise birthday parties. While, unsurprisingly, she gets very flustered when things don't go according to her plan and must struggle to switch gears, when it's a special occasion different rules seem to apply.
I think I may have an idea as to why a J, particularly an SJ, could actually like surprises under certain circumstances. My mother, in true SJ form, turns everything into a duty in her mind. She likes to plan out everything that needs to be done, and then duely worry about getting it done untill it's finnished. Her daily list or schedual acts as an invisible taskmaster nagging her when things are not crossed off and patting her on the back once they are. She feels a sense of satisfaction when everything is finnished that she has determined needs to get done. Even if it was something "frivolous" like walking down to Dairy Queen for a cone, she approaches it more like work than play, and seems to be just as satisfied by marking it off the list as she was by the actual activity.
And this is where surprises come in. I think someone like my mother can like surprises because they don't have to do any of the planning and worrying. Thus the activity feels more like play.
SJs have a hard time approaching things in a carefree or playful way, and they usually feel guilty about planning things they enjoy for themselves. They have an incredible sense of duty toward others, and may do a lot to make sure others are happy, but don't feel comfortable spending time on things that aren't in some way an obligation. The fact is that they need others to plan their fun for them in order to really be able to enjoy it. The minute they get their hands on the planning, they have issues with needing to rationalize the fun, with worrying about everything going smoothly, with trying to make sure everyone else involved is taken care of even moreso than themselves, and turning the whole thing into a chore or obligation in their minds. Some of them may feel bad about accepting the kind intentions of others, but they are much more likely to let go and enjoy things when they realise that this time someone else is looking out for them. SJs are used to feeling like they have to do all the work while other people play and procrastinate, so planning a fun surprise for an SJ will remind them that people do remember and appreciate them. And if they just can't get past the need for a sense of duty, they can always feel obligated to have a good time so that everyone else's efforts won't be in vain.
An important detail to note is that in the event of a surprise party or outing planned for them, a J person can still rest assured that there is a plan, that someone knows what's going on and how it's all going to work. This helps them a great deal, and they can usually abdicate their need to keep controll of their life to the person who has kindly planned this event for them. They trust this other person to see that everything runs smoothly. They may also have, in a sense, planned for someone to surprise them if they know a special date is coming up, and thus may not be totally thrown off guard.
