The Schlieffen Plan had failed as the Germans didn't realise the fact that Russia could mobilise quickly. The development of transportation shortened the time taken for them to come to the Eastern Front.
Belgium was supposedly neutral, but when faced with the German army, they fought back and didn't allow Germans to pass through to get to France. This slowed them down -- a devastating setback for a time-sensitive plan.
Britain came to Belgium's help, which meant that it took more time for Germany to advance through Belgium to get to France. Belgium had the support of a powerful army now.
Before the Germans launched the Schlieffen Plan into action, the devisor of the Plan, Alfred von Schlieffen had died. There was no on to seek help from when the original plan failed.
R.I.P Al von Sch
The new General, Von Moltke, reduced the troops in the East and changed the route to go through Belgium instead of Holland. The fact that they didn't stick to the plan made them more defenceless in the future, as there was no set plan.
Despite Germany's last push to attack France, they failed. This led the Germans to sign an armistice, in order to put an end to the war. This was one thing that Germany had been hoping to avoid.