Why do things happen in threes?

Washing machine first to give up (new one coming Wed), central heating next (new pump fitted today so I've now thawed out! )Yesterday a man drove into the back of my car so hope it stops at three! Insurance have been great and as he admitted his foot slipped off the brake on to the accelerator my car will be taken for repair on Wed and a hire car will be delivered all at his insurance's expense!