Passage: Across time and space, the Doctor's many incarnations often find events that pique their curiosity and try to prevent evil forces from harming innocent people or changing history, using only ingenuity and minimal resources, such as the versatile sonic screwdriver. The Doctor rarely travels alone and often brings one or more companions to share these adventures. These companions are usually humans, owing to the Doctor's fascination with planet Earth, which also leads to frequent collaborations with the international military task force UNIT when the Earth is threatened. The Doctor is centuries old and, as a Time Lord, has the ability to regenerate in case of mortal damage to the body, taking on a new appearance and personality. The Doctor has gained numerous reoccurring enemies during their travels, including the Daleks, the Cybermen, and the Master, another renegade Time Lord.

Question: How often does the Doctor travel alone?
rarely