Doctor Alexandre Manette had been in jail for 18 years before Jarvis Lorry, Monsieur Defarge, and Lucie Manette, his daughter, came and took him to London, or as they referred to it many times, "recalled him to life". At some point in this 18 year period, he turned to making shoes nonstop, it was all he could think about. It eventually became a comfort to him. After five years, we can see Dr. Manette is more in tune with his surroundings. He has quit his shoe making and is very close to his daughter, Lucie. Lucie is symbolized as "The Golden Thread" not only because her hair is golden, but because she is the thread that is holding Dr. Manette's sanity together. Their relationship clearly means the world to him. After Lucie and Darnay's wedding, Manette had trouble coping. He was afraid that he would be separated from Lucie. For a bit, he relapsed into old habits and starting shoe making again. Mr. Lorry and Ms. Pross were worried by this, so when he was away, they destroyed his bench. It is clear that Dr. Manette is simply content with either Lucie or his shoe making. These things keep him in a happy place, and Lucie especially gets him out of a certain funk that the jail put him in.
When Lucie and Dr. Manette saw each other for the first time. Lucie thought he had been dead all this time.
Dr. Manette with his beloved daughter, Lucie, and her husband, Charles Darnay.
Mr. Lorry and Ms. Pross destroying Dr. Manette's shoe making bench