Robespierre's downfall was due in part to his own self-righteousness and inflexibility. He was unwilling to compromise or adapt his ideals in the face of changing circumstances, and this led to his alienation from many of his former allies. He also made the mistake of assuming that the French people would blindly follow his leadership, even when his policies went against their own interests.
In the end, Robespierre's Reign of Terror backfired and led to his own execution. He became so obsessed with eliminating his enemies that he eventually turned against even his closest friends and supporters. This paranoia ultimately led to his downfall, as he was eventually overthrown by a group of his former allies.
Robespierre's tragedy is that he was a man of high ideals who ultimately became corrupted by power. He started out with the best intentions, but his desire to create a perfect society ultimately led to his downfall. He is a cautionary tale about the dangers of extremism and the importance of compromise and moderation in political life.