First, there is the problem that it seems to be quite evident that certain scenarios requiring the cooperation of all or most of the individuals in a group would provide benefits for everyone far in excess of what they would be able to do privately.
Good examples are elections, roads, water supplies, river levees and other large investments.
Yet, at the same time, it is obvious that for a particular individual, his or her maximum return is obtained by making no contribution - that is, freeriding. For example, if the levee could possibly break, the individual would be best served by not contributing to the sandbagging at the main levee but instead working on defenses around his own home. On a national election, one vote cannot possibly determine the outcome of the election. Or if it didn't break because it had at least 50 more than it needed, my contribution would again be useless. Massive non-cooperation results in a breakdown of many group activities that would be useful.