Peace and human rights have powerful enemies, so a peace prize that was always uncontroversial would clearly not be doing its job. And sure enough, the Norwegian Nobel committee has waded into controversy again this year with the award of the peace prize to jailed Chinese human rights campaigner Liu Xiaobo.

The least controversial awards tend to be those to individuals or organisations in recognition of ongoing work for peace: the international committee of the Red Cross, for example, has won the prize three times. Former Finnish president and international mediator Martti Ahtisaari was a popular choice in 2008. (The complete list of peace laureates is here.)

But even there controversy is far from unknown. Mohamed ElBaradei and the International Atomic Energy Agency had some prominent critics when they were chosen in 2005, as did Al Gore and the Intergovernmental Panel on Climate Change two years later. Some recipients have credentials other than those that are officially recognised: last year’s award to Barack Obama made no mention of his one outstanding contribution to world peace — the fact that he prevented John McCain from becoming president.

Other laureates are selected for specific achievements in promoting a peace agreement or helping to settle some long-running dispute. Because, unlike the other Nobel prizes, the peace prize tries to be reasonably contemporary, some of these awards can look less appropriate with hindsight. The 1998 prize for the peace partners in Northern Ireland has held up fairly well, but that of 1994 for the Oslo accords in the Middle East now looks shaky, and 1973’s award to Henry Kissinger and Le Duc Tho was dubious even at the time.

But the most interesting awards are the ones to advocates of a cause that has not yet succeeded, who are working on behalf of the oppressed in difficult and dangerous circumstances. Some choices have been triumphantly vindicated, and the recipients, controversial figures at the time, went on to become national heroes: Martin Luther King (1964), Andrei Sakharov (1975), Lech Walesa (1983), Desmond Tutu (1984), José Ramos-Horta (1996). In each case, the peace prize gave not just moral encouragement but a valuable addition of international publicity to their cause.

Others, however, are yet to see success or even significant progress for their cause. Tibet’s Dalai Lama (1989) is still in exile; Burma’s Aung San Suu Kyi (1991) is still under house arrest; Iran’s Shirin Ebadi (2003) judges it unsafe to return to her own country. And going by China’s reaction, there is not much chance that the Nobel prize will do much to help Liu Xioabo’s chances of release.

The most inspirational laureates all became famous by their own efforts, not for winning the Nobel prize. Many winners remain obscure, while such greats as Mahatma Gandhi and Vaclav Havel were never honored, and Nelson Mandela won the prize only after his release.

Certainly a Nobel can direct much-needed attention to a cause. But the problem with China’s dictatorship is not international ignorance, but a wilful international refusal to pay heed.

It’s very much to the Nobel committee’s credit that it did not feel bound by that refusal. But despite its support, Liu Xioabo’s struggle may still be a long one.