We have hydrochloric acid reacts with an alkene. Now, two different pathways are possible. In other words, this lewis base can take this H atom and follow pathway one, in which the H atom goes on this side of the carbon. So on this carbon, it attaches to the second carbon of the double bond. Or it can take pathway two, in which the lewis acid takes this H and attaches that H to the other side of the double bond to this carbon. So we can either take pathway one and form a tertiary carbocation, or we can take pathway two and form a primary carbocation.