It is possible to state, without exaggeration, that the Treaty of Versailles was one of the great diplomatic disasters of history. The chief effect of this treaty is the rapid slide into disorder and totalitarianism of the German state, and an indirect cause of the Second World War. However, several other stipulations and effects of the of the treaty also clearly demonstrate its inherent unfairness.
One stipulation of the treaty was that Germany was forced to pay reparations to the Allied powers. This was difficult for a variety of reasons - the economy had nearly collapsed from years of blockade, and the amount was so large that it was deemed impossible to pay. Germany was barely capable of feeding its own citizens by the end of the war, and the idea of reparations only further strained the economy. The 'solution' only worsened the problem - the debasement and hyperinflation of the German currency. Simply put, in order to pay the stipulated payments, the currency was made worthless. This only worsened the woes of the people, as their savings were made worthless, and prices for food and other necessities soared. The paper bills eventually became so worthless that they were used as wallpaper, or bundled up and burned - they would not be worth the cheap paper or firewood used otherwise.
Another effect of the treaty was Germany's supposed demilitarization. Germany, ever since its formation in the 1870s, was a militaristic state. The military was considered a prestigious and necessary branch of the German state. Once the military was reduced to a pitiful state, the nation as a whole felt emasculated. Even before Hitler's rise to power, German generals, such as Hans von Seeckt, conspired to begin the rebirth of the military - it was simply impossible to hold the state together otherwise.
Yet another ineffectual provision of the Treaty was the foundation of the League of Nations. This own organization was an even more ineffectual version of the United Nations...