One year lease contract

I have just moved to brussels and am looking to rent an apartment here. I was wondering whether anyone knew the answer/has had personal experience with the following - If you sign a one year lease and for whatever reason have to leave the country or decide it is not the apartment for you, how easy is it to get out of the contract? Is it a case of finding someone new or paying a few months extra rent, or is it simply not possible to get out of a 1yr contract?