My friend Ben (via his awesome tumblr) pointed me towards an article in National Geographic that highlights an empirical study on the impact of privilege and luck.
In order to study this topic, they looked at four different ways of giving out small levels of success - small amounts of funding on Kickstarter, positive ratings on Epinions, signatures on Change.org petitions, and awards to Wikipedia editors.
(van de Rijt et al, 2014.)
Those who were randomly given a random initial boost went on to do significantly better than those in the control group. Whether this is because the success attracted notice by others or more because the success made those granted positive feedback try harder isn't clear (except in the case of ratings, where additional effort would be less likely to impact a comment that is already made).
But whichever effect dominates, the implication for what to do when you have friends embarking on projects is clear. Helping them a little bit can have a large impact on their eventual success.
The study also found that large amounts of help were only marginally better than small amounts of help. This implies that helping four friends a little bit is probably going to have a higher return than spending four times as much effort helping just one person.
This also explains why networking properly - helping lots of people you meet in little ways - can have a large impact in the long run.