These days having few friends frequently signals maturity or coolness—someone who doesn’t add everyone they’ve ever met to look like they have lots of friends.
I think the sweet spot is between 10 and 200 - go over that and people tend to imagine ‘there’s no way he could actually have that many friends, he just adds people at random and cares too much about popularity’.
Edit: Having said that, I just went back to my fb, which I no longer really use, and I’m on over 350. But largely that’s because I’ve had it for a long time and not removed people I no longer see or have any real intention of seeing, so I don’t only have actual friends as friends either.
Judging by some of the attitudes I have heard from my friends about getting a flu jab (similar to Lumifer’s comment), I have found that it is actually more effective to encourage people to get flu jabs for the benefit to others via herd immunity, rather than by emphasising the benefit to them.
I don’t know if this is maybe some kind of ego-bias in that healthy people underestimate their chances of getting sick, or that doing something for you doesn’t get you fuzzies, whereas doing it to help sick people and babies does.
Of course I am in a country that won’t pay for healthy people to get the flu jab, but will pay for their hospital stay if they get sick enough to be hospitalised. The NHS does, however, pay for elderly people and people with most long-term health conditions (including asthma and diabetes) to get the jab.
I imagine that the NHS has done a cost-benefit analysis of the costs to itself to pay for healthy peoples’ flu jabs versus their hospital stays if they do get sick, but I don’t know if they have.