It is actually a saying in German: "erstens kommt es anders und zweitens als man denkt." it sounds great and it plays with the words, but basically it means that you never know how things will turn out.
you can make a 1000 plans and try to control every single step along the way, but there is no guarantee.
so everytime sth goes wrong, i remember that and relax. it is just the way life is.