Kyriakos Mitsotakis scored a significant victory on Sunday. The truth is that pundits thought him the outsider and had estimated the odds of him winning as very small. The election for a new leader at New Democracy, however, showed us two things. First, that being underestimated can be a huge advantage in politics and, second, that it is a mistake to underestimate how voters think.

Mitsotakis’s candidacy drew the interest of people who are serious about politics but abhor petty party workings. It also drew the core of those who voted “yes” in July’s referendum over whether Greece should agree to another bailout deal with creditors or not. Many of those people would never vote for New Democracy and cast their July ballot with a heavy heart, but they understand the need for a strong opposition. Those two groups were, of course, joined by traditional supporters of the conservative party who were concerned about the party joining forces with leftist Prime Minister Alexis Tsipras. Mitsotakis’s contender, Evangelos Meimarakis, did himself harm by giving the impression that he was not interested in reaching real consensus with the government but was engaging in tactical maneuvers instead.

The new chief of New Democracy faces a lot of challenges ahead. He has already come under fire on numerous fronts and the blows will continue, both above and below the belt. So far he has shown that he can take it, but the higher you get, the more your true mettle is tested. While Mitsotakis can draw voters from the center and middle ground, he could just as easily lose support from a portion of New Democracy voters who consider him to represent the country’s political elite. In this respect, it is important that he was not elected in the well-heeled Athenian suburbs of Kifissia and Glyfada, but was in places like Thessaloniki and Kastoria.

What Mitsotakis needs to do now is rid the party of the rot that has built up but without making its supporters feel that he is tearing it apart.

His election, moreover, has been seen favorably abroad as the young politician is regarded as a credible alternative to the leftist-led government. The notion that Tsipras is the only game in town will gradually fade even though his honeymoon with Brussels will likely continue a while longer.

Mitsotakis has taken on a huge responsibility. There is no doubt that he has the systematic approach, the knowledge and the sensibility required by the circumstances. He also scored a success that few thought he could achieve. Now he needs to win the support of voters beyond the party base and second, to brave the next few months, which promise to be very troubled indeed.