As per the title, the question is can you role-play by yourself? It seems to the novice roleplayer that a good part of RP is done solo, in general at least. Maybe I'm wrong but it seems logical that you would devise your character and your back-story by yourself. Perhaps your character's story is shaped by others, but the seed, the core of the story is created by the player alone.
Once this back-story, or the seed thereof, is established, it seems to me, again as a novice, that roleplaying is essentially a group activity. It seems hard to create a meaningful character without at least some kind of interaction. My thoughts are drawn to a female troll who is always behind the bar in Silvermoon City on one of the most famous EU RP realms. Were she to never have any customers, would she still carry on working behind the bar? Does her roleplay rely on the presence of others?
And does yours? Have I completely missed the point here? It's highly possible. Or maybe it's just that roleplaying is more fun with others, most of the time at least. What do you think? Could you, hypothetically, roleplay in a satisfactory way without ever interacting with another player?