According to a theory called the Dunbar Number humans have limits on how many friendships they can sustain. On average, people have about 150 friends in their social group, but only about 15 of those are close, long-term confidantes. The rest are more casual acquaintances. Recent testing of this theory found the same thing – despite social media and multiple online 'friends'. Each type of friendship plays a role. You may get support and stress relief from a close friend, while work colleagues, neighbours and online friends also keep you connected, active and engaged.