What is it?
Some people feel that others in the group will leave them to do all the work while they take the credit. Because people do not want to feel like the "sucker", they wait to see how much effort others will put into a group before they put any in. If all the members try to avoid being the sucker, then everyone's effort will be significantly less than it would be if all of them were working as hard as they could.
This is called the sucker effect. This effect can lead to the situation where everyone wants to be sustainable, but nobody acts out of fear of being a sucker. “Why would only we want to focus on sustainability"
Show that there are companies that make the sustainable choices; that there are succesfull examples out there.
Avoid bad examples of companies that don't act. This can lead to cynicisme.
This effect decreases strongly if there are examples of others making sustainable choices.
Read more about social loafing and the sucker effect on Wikipedia
Norbert Kerr (1983). Motivation losses in small groups: A social dilemma analysis. Journal of Personality and Social Psychology, 45(4), 819. Link
Denise Baden (2014). Look on the bright side: A comparison of positive and negative role models in business ethics education. Academy of Management Learning & Education, 13(2), 154-170. (doc) Link