When someone is secretive about themselves and their activities the assumption is always either they're trying to conceal something hideous or maybe they have some kind of treasure they don't want others to know about.

However, it could very well be that person simply values their right to privacy.  And it's not because they're hiding dead bodies in their closet or a meth lab in their shower, nor are they trying to keep from the authorities any late-night rendezvouses with some underage secret lover.

Each person has their own idiosyncrasies, prejudices, viewpoints and temperaments.  And someone who might consider something you feel a strong passion for to be of a trivial nature, quite frankly, should not be present where you are while you're engaging in some creative venture or passionate hobby as they could become invasive or hampering, interfering with your efforts either by trying to infuse their own elements into YOUR project or just getting in your way:  messing with your stuff or making snide and snarky comments and behaving all-around petulant because they simply don't understand (because it's not what they're into themselves).

That's ANOTHER argument pro-privacy.  The need for your own area in which you can do and be your honest self without obstructions or impediments.  The right to decide when and where you deal with personalities who are only harmonious under limited conditions while discordant in other settings.
A place where you can act freely while doing things that are important to you.
The right to set your own boundaries and to keep domineering personality types at bay.