Why did peace negotiations break down after the oslo accords?

The Oslo Accords simply did not take into account factors that would influence its interpretation. For example, the Cave of the Patriarchs massacre, in which at least 39 Palestinians were killed by a single Israeli gunman (who was beaten to death once he run out of ammunition), is often blamed for undermining Palestinian trust in the process. Similarly, the expansion of Israeli settlements (although the Oslo agreements, sillily enough, stipulated no such ban) and blockades caused the deterioration of economic conditions, and much frustration for Palestinians. These factors caused a drop in support for the accord and for those who supported it. However, the PA acknowledges that the settlements have actually provided 12,000 temporary jobs to Palestinian construction workers.
And on the Israeli side, the increase in terror attacks and refusal of the insurgency groups such as Hamas to respect the Oslo agreements caused much frustration for Israelis who lost faith in the Accords as well