Most people are very consistent in their lives.
If Tom gives to a charity one year, the charity can usually plan on him giving the next - they just send the envelope. If he buys a new Triumph Spitfire when his old one is three years old, after three years he will probably buy another one, and the salesman will be waiting with a brochure in his hand. He will go home to the same house and sleep with the same wife every night. If he deviates from this pattern, there is a good reason. A lot of inconsistent characters march through screenplays.